The only downside to killing them after they have been "converted" is 1) one or more of them may get destroyed by hostiles on that level, and 2) it's quite easy for a low level PC to destroy them one-by-one using the chamber doorway to restrict their advance and a significantly tougher combat challenge when all four can flank. (Then again, I can't remember if a forced attack on 1 caused all the others to revert at the same time.) I generally forego the gem XP because, in the big picture, that 50XP is paltry.
Oh, and MrZork is point on target about the XP drain... the bigger your party, the less XP per kill so unless you can prevent them from wandering (i.e. immediately attack after placing the gem), they will penalize way more than the gem XP amount.
Modifié par HipMaestro, 16 octobre 2010 - 02:32 .