[RPG] Should PCs receive XP for enemies that die to friendly fire

I think that for this one you're going to have to step outside of the rules and say that the combatant in question stabs himself in the chest or other extremely vital area. 4e combat rules assume that you want to do damage and not take it; I don't think you are even a legal target for your own attacks. 4e may have tighter and more encompassing rules than earlier systems, but that's no reason to forget Rule 0 when it comes to things that are out of scope for the combat or skill systems.

EDIT: The OP changed the question to be more rules-based, so here's my effort. I'm using the Rules Compendium for this.

• By the rules, a PC can attack themselves, since MBAs have a target of "creature" and an attack with a range can legally hit someone in your space.
• It's not even clear that monsters can hit PCs, if you take the most pedantic reading; I cannot find a definition of the legal target set for monster basic attacks. I would assume "creature" here, but that's an assumption.
• Even if you can blind yourself by shutting your eyes - this requires Rule 0, because shutting your eyes is not a defined action - the total concealment penalty is greater than the combat advantage bonus.
• You cannot "declare" yourself helpless as such. However, if you could, you could attack yourself with combat advantage; helplessness only results in granting combat advantage and nothing else! A more normal, but Rule-Zeroed, approach would be to say that you cannot attack, in which case you can't attack yourself either.
• You cannot coup de grace yourself; the rules specify an adjacent target, not one at Melee 1, and the definition of adjacency uses two squares. A Large creature would presumably be adjacent to itself, however, since it is in four squares.
• None of the other status conditions causes bonuses to damage, and aside from coup de grace, I don't know of any of the normal combat actions that cause bonus damage.

I think the rules-based answer is that you (i.e. the troll) can keep MBAing yourself until you drop, but you can't really go faster than that without Rule 0.

I've had similar issues, and been experimenting. Here are some of my findings:

• ALWAYS have strategies in mind. A squad has two, maybe three pre-determined strategies and the ever-available "every man for himself" panicking. They engage with one strat, move to the other if the situation calls for it, and break ranks when appropriate. This keeps me active instead of trying to think of their actions each round. It's the middle of a battle, folks don't have time to make the optimal choices; they'll stick to their training.

• Surrender. Soldiers don't want to die. PCs can force a bloodied NPC to surrender with Intimidate, but a soldier who's just seen three of his buddies get fried by divine fire probably doesn't need to be explicitly told to give up. It's possible to cut fight time in half this way, though it still doesn't make the wait between turns any shorter each round.

• Giving NPCs immediate actions and "start of PC's turn" effects instead of a lot to do on the NPC's own turn helps speed things up considerably.

• The more NPCs I have, the simpler I make them. If I'm going to have more than three copies of a given NPC, I don't want that stat block to have more than three or four actions or things to keep track of.

• In line with the above, minions. I use them very rarely because they encourage metagaming, but they remove damage calculation entirely which speeds up combat a lot. Conscripted soldiers are likely to drop and play dead the first time they're hit, so that's a justification for minions in your scenario. Give your minions an on-death effect like grab or difficult terrain; it makes minion-popping require more strategy than "bust out your AoEs."

• Often I "cheat" and make my non-minion NPCs deal set average damage without die rolls.