I feel like it depends also which kind of key level it is. If it is a really high key (Like 10+ this season) you probably not doing it to farm loot or crest, and mostly just because of making it in time, therefore I think it is alright to leave earlier if it looks like it is not happening
But if you playing a 2+ and such, then leaving because of one or two wipes, then that is a bit yikes. It might not be the best key, but you still get crest + loot at the end. It sometimes takes a while to even form the group if you are a DPS, and someone leaving that group after a wipe feels really bad