As a preliminary note, a good solution to this problem will (as usual) involve talking to your players. Ask them if they think this is even a problem, and if so, what kind. You may find that they enjoy being reckless and don't mind dealing with the consequences, even if that means inaction or even death for their characters. If so, congratulations: you're all set! But if they don't want to be unconscious and bored, read on.
You can try different things to keep them entertained, like having them run NPCs, narrate the combat to make it more epic, or take notes for posterity. If your players are flexible, that may work, and they may even enjoy the change of pace. (Though honestly, in my experience once they're stabilized it's usually a good time for a bio break to get more drinks for everyone or take care of other necessities, which should resolve the situation nicely unless it's a really long fight.)
However, most players are at the table because they want to play their characters. (Not all of them, but most of the standard motivations require being able to influence the game in some capacity, and most of those involve investment in a specific character.) If that's true, then no substitute will ultimately be as satisfying as being in there with your own character, mixing it up.
So if I could back up a bit, I would ask a different question, namely, why is this situation occurring so frequently that you have to ask?
If PC's routinely get KO'd, I suspect one of three things is true: A) your PC's are low level; B) your PC's are employing bad strategies; or C) your encounters are structured in a way that causes a lot of KO's, possibly because you're using Glass Cannons (warning: TVTropes).
A) should resolve itself pretty quickly. B) might resolve itself as your players learn better strategies, but you may need to ask if they want any pointers. If it's C), though, you can fix this by adjusting your tactics, both in building encounters and how you run them. A plan failing because "You didn't even dent her armor!" can be as spooky as one failing because they spotted you and stabbed you. (Of course, if you go too far with defensive enemies, fights can drag on forever, but sometimes people have to be defeated in a particular way that requires a little in-game research or experimentation.)
More importantly: if your boss fights are deadly and/or you've successfully cultivated an atmosphere where they feel deadly, when a PC does drop your players should be scrambling to get them back up so they don't lose the advantage of numbers (not to mention, y'know, keeping them alive). You've said the party doesn't have a ton of healing, but you can influence that by pointing them towards Goodberry and other useful spells and abilities, adding an NPC, or just giving out healing potions as loot (something that's working pretty well for 2 groups I'm in with relatively little healing). If people are watching each other's backs, a PC shouldn't be down for more than a round or so.
If you take the above into consideration, I think you can probably settle into a rhythm where this isn't too much of a problem in the first place.
Tell him the truth, because that's what friends do
Sometimes, talking around or avoiding an issue increases trouble, rather than decreasing it. This looks to be a case of that happening.
You said this in a comment.
The main thing is, the DM is a good guy, but his girlfriend is adding
some complications to the group because he is understandably trying to
make her enjoy the game. His plots move slower than DragonBallZ
seasons, and the group wants another player, who is a seasoned AL GM,
to step in for some faster/more reliable and on point gameplay. The
player GM'd a one-off last weekend that was fantastic, and we want him
to keep going.
- The point of getting your group together is to have fun
- What was fun was the one-off you just did. What wasn't fun was that other thing.
- Point out (as a group) that it is obvious to the rest of you that she's not all that into D&D. You all don't want to force her to have that kind of fun, and maybe he needs to know that you (as a group) don't feel a desire to try and persuade her to have fun in that form: a D&D game. You can't force fun like that.
Now for the payoff, in your own words, you need to tell DM something like this:
- We are all in this to have fun, and your DMing has not been fun for the understandable reason that your priority is her: we get that, she's important to you. We'll be playing the next session with the new DM, and we hope you'll join in as a player if your relationship allows. If not, also understood as relationships are important.
Including a thank you for stepping up to do some DMing is certainly in order.
- In that event, if she accompanies him anyway, but he's a player, it no longer becomes an issue since the DM in question isn't constrained by "trying to serve two masters."
- Having seen a few similar dramas play out where game and relationship clash, the longer you let it fester the worse it is for your group.
That's about as tactful a way as you can put it. By not speaking up and clearing the air, you risk falling into the unfortunate trap of "bad gaming is better than no gaming." (It isn't).
And the truth will set you free.
Good luck. For a similar but different problem that has to do with interpersonal dynamics, you might want to take a look at this Q&A.
@yo' suggested the following:
Speak to him without her presence to give him the opportunity to solve
his relationships. With her presence, things could go wrong so easily
on the spot.
Depending upon your assessment of how she gets along with the game group, this is solid advice and likely the best approach.
A related issue about "trying to have it both ways" when gaming and relationships collide.
Your DM is experiencing the problem of "having it both ways" by both being able to have fun by being a DM, and spending his free time with his significant other at the same time ... when she's not all into that form of free time (group fun, versus one-on-one interaction). Quite frankly, I discovered that I had to make a choice (wife in this case) when I discovered after a few tries that she just wasn't into it (it = D&D) though the kids loved it. What happened for me was that I first curtailed and then let go of D&D for ... about a decade. Why? Because relationships are important, and the marriage is the one that got priority.
Best Answer
If something is causing you to not have fun, you can tell the DM: "Hey, this thing is causing me to not have fun, can we do it differently?"
If I were playing at your table, I can tell you that two of the things you describe would cause me to not have fun, and the rest would seem sort of eccentric but irrelevant. I would say:
"Hey, in that last scene, we all kind of sat there for half an hour with nothing to do, and I felt sort of bored. Could we try to make sure that more of us are involved in future scenes?"
And: "Hey, in that last combat we did, we didn't roll initiative, and I feel like my turn was skipped. Could we roll initiative in future?"
I am a DM, and I listen to this sort of thing, and I would expect other DMs to listen to this as well.
For the other issues you describe, like deciding when to call for a skill check or a save, I recommend that you not worry about it.
In particular, for that Arcana check you describe, you're technically correct that it's the DM's job to name the skill check, and not the player's. But, once the player has decided to look at the amulet, everyone at the table knows what check is going to happen, and it doesn't seem like it's worth arguing over who should be allowed to speak the words "arcana check" first.