While naming and shaming isn't allowed I can't remember the guy's name anyway, so I'd just say this is something to watch out for, unless it doesn't go here in which case it'll be moved.
Here recently I decided to see who would join an open party for The Legion danger mission in tier two, and a single person joined. The first floor went somewhat well, a death or 2 here and there. The second floor however, this other party member died in the first room, got up to finish, then after going right, sometime a few minutes later died again. After staying dead for some time, long enough to clear out the party button on that side, he says he needs to go away for a bit, from his computer he said. I don't think much about it at first, but then, nearly forty minutes later, he's still dead, and I'm walking into the final room after having to clear out the entire other side by myself. At one point I start to wonder why he hasn't been kicked yet for being "away" for so long, or if he's even really away at all. By the last room, I'm starting to wonder if this person is just waiting for a free trip to some treasure, despite knowing he won't get any drops from loot on the way there, but rarities only drop from boxes, and the free revive would kick in the moment we hit that floor. Rather than feel like I was just being used to carry someone on a free trip to orbs and sparks among other things, I kicked him out of the party during one of the waves in the final room, finishing by myself and leaving him behind.
While I am aware that this could have just as easily been someone who may actually be busy and constantly checking back on their computer to make sure they're not kicked while they finish whatever it is they were doing, it also occurred to me that some, more knowledgeable players may try this exact method to exploit entire groups or single players during runs at an attempt to get free rarities with no work on their part.
This is obviously a complaint, but it should also be a warning to watch out for things like this, simply because newer players may not know as much about how the game works. That's not to say every member who dies and stays dead is doing this obviously, but if someone is going to join a party and then vanish for nearly an hour, it's going to seem a bit strange.
"wonder why he hasn't been kicked yet for being "away" for so long"
Steam overlay
"then vanish for nearly an hour"
Maybe your teammate wanted to spectate you? See if you could complete the mission with the hp bonus for mobs (party of two or more). lots of ppl do the exact same thing to me too. Since i wear "bad armor" in all my runs.
Yep. It does seem strange, but i've got to ask, did the player give you any notice beforehand? A good solution is to mostly go solo. That way you won't need to worry about people "taking up your time"