"Doctor! It hurts when I move my arm like this!" "So don't do that, then…"
On page 168, the rules discuss what it means to be "Taken Out" — and, in particular, what the circumstances are like in groups where Taken Out equates to "dead":
So, if you think about it, there’s not a whole lot keeping someone from
saying, after taking you out, that your character dies. If you’re talking about
a physical conflict where people are using nasty sharp weapons, it certainly
seems reasonable that one possible outcome of defeat is your character getting
killed.
In practice, though, this assumption might be pretty controversial
depending on what kind of group you’re in. Some people think that character
death should always be on the table, if the rules allow it—if that’s how
the dice fall, then so be it.
Others are more circumspect, and consider it very damaging to their fun
if they lose a character upon whom they’ve invested hours and hours of
gameplay, just because someone spent a lot of fate points or their die rolls
were particularly unlucky.
We recommend the latter approach, mainly for the following reason:
most of the time, sudden character death is a pretty boring outcome when
compared to putting the character through hell. On top of that, all the story
threads that character was connected to just kind of stall with no resolution,
and you have to expend a bunch of effort and time figuring out how to get
a new character into play mid-stride.
That doesn’t mean there’s no room for character death in the game, however.
We just recommend that you save that possibility for conflicts that are
extremely pivotal, dramatic, and meaningful for that character—in other
words, conflicts in which that character would knowingly and willingly risk
dying in order to win. Players and GMs, if you’ve got the feeling that you’re
in that kind of conflict, talk it out when you’re setting the scene and see
how people feel.
At the very least, even if you’re in a hardcore group that invites the potential
for character death on any taken out result, make sure that you telegraph
the opponent’s lethal intent. GMs, this is especially important for
you, so the players will know which NPCs really mean business, and can
concede to keep their characters alive if need be.
The Rules As Written answer, therefore, is that the GM has made a poor choice in setting the stakes that way, and should reevaluate the desires of the NPCs in question.
However, you're asking who bends when the unstoppable force meets the immovable object. In this case, the rules strongly suggest that the GM does -- the ability of the player to concede in this circumstance means that if he or she wants her character to survive, the character does. It's up to the group, as you quote above, to come to a consensus about how this happens.
In the situation you describe, I might have the bobcat-people maul the character and leave him for dead, rendering him wounded but capable of recovery with medical attention later. But at any case, once the decision is made to concede, it's a good time to stop and check in to make sure all parties are on the same page regarding the story being told here.
You are the DM, you can say No, although "No, but ..." also works
You are not required to change your world to accommodate a single player. What are the other players creating, as characters?
Saying yes to the android theme is workable
For the "android" theme, consider making the PC a construct; it is a creature type in D&D 5e. While it's a matter of homebrew, you can work on this together with your player using the Warforged1 from the Eberron UA as a starting point. This homebrew needs to be a collaborative effort; you get the final say since it needs to fit into your campaign world. (Perhaps a permanent curse/magical effect happened around the time of the character's birth?)
- Your player is an experienced DM; the work on this homebrew won't be a burden on you; that said, you need to do the final check on the homebrew to make it fit into your world so that it's not overpowered, nor unbalanced, compared to other PCs.
You two can have some fun creating this homebrew race. If you don't want to do the gunslinger class, then suggest to the player (perhaps) a hand-crossbow using character who takes the crossbow expert feat as your world's version of handguns.
CROSSBOW EXPERT
Thanks to extensive practice with the crossbow, you gain the following benefits:
- You ignore the loading quality of crossbows with which you are
proficient.
- Being within 5 feet of a hostile creature doesn’t impose disadvantage on your ranged attack rolls.
- When you use the Attack action and attack with a one handed weapon,
you can use a bonus action to attack with a hand crossbow you are
holding. (PHB p. 165, w/errata correction).
The "mafia" connection can be a trade guild, merchants' syndicate, a thieves' guild, a druid conclave working to roll back the overbuilding in certain areas, or a cult run by a Trickery cleric (or a Warlock) who is trying to slowly wrest power from a wizard's conclave. They sky is the limit regarding secretive and criminal organizations.
If you say "No guns" stick to your (no) guns ... :)
Your player appears to want to play in a different campaign than you are running. That happens sometimes. Ask him to create a character that fits your campaign. Your player's character needs to fit in with all of the other characters in the campaign that are being played by the other players. Making this a joint homebrew project can be rewarding for you both, and fun, as long as the party fits together well enough.
D&D 5e's basic model is that of a team of adventurers. Does this player want to be part of the team or not? You both need to clear that up before the adventures start. Likewise, he needs to discuss that with the other players.
"No, but..." becomes "no to the guns but yes to the android theme"
1 From the UA Eberron
Warforged
Although they are constructs, they have much in common with living creatures, including emotions and social bonds, and perhaps even souls.
Ability Score Increase. Your Strength and Constitution scores increase by 1.
Size. Medium.
Speed. Your base walking speed is 30 feet.
Composite Plating. Your construction incorporates wood and metal, granting you a +1 bonus to Armor Class.
Living Construct. Even though you were constructed, you are a living creature. You are immune to disease. You do not need to eat or breathe, but you can ingest food and drink if you wish. Instead of sleeping, you enter an inactive state for 4 hours each day. You do not dream in this state.
It's a good place to start. Also, since this answer was written, the Warforged become an officially published class in the Eberron: Rising from the Last War setting book.
Best Answer
Everyone is focusing on mechanical aspects, but this in a backstory so we don't want to start a game with mechanical downsides and then get more if they die again. I suggest a roleplay downside:
PTSD: The character is now traumatized by dying, they are afraid of dying again or have flashbacks to it.
Losing oneself: The character comes back lesser than before, GoT does this a lot, they come back but something is missing.
It affects others: Maybe the character didn't think it was a big deal but others did, even if you know it still would hurt to see your friend murdered, or maybe they didn't tell anyone and now everyone is mad at them.
But if this is a race known for this then nothing normal would make it a death worthy of mention since dying is a normal situation for them, so my last suggestion is:
Tie it into the campaign: maybe the character was killed by your main villain or one of their right hand men. Maybe they died learning a secret important for the campaign, maybe they died while defecting from the villain's side.