I have had people leave even w/o a wipe. We had healer leave in AK because the first boss took too long in his estimation. Same story with a tank in another party. In the first case the tank was a little inexperienced (had trouble holding agro on multiple mobs), but overall he did okay and tried to improve. Anyway we picked up another relic +1 sch to replace the one that left. He was very helpful and blasted through AK, I think he did more DPS than either me or the mnk. Anyway, it turned into a positive in one case.

Sometimes even winning isn't enough these days. I did leave a WP party due to the sch being severely undergeared, to the tune of level 7 accessories (except DL wrist of striking). We wiped before the first boss. I figured they would need someone that could provide more help than I could give. My BRD is geared okay, but nowhere near enough to carry the party.