Me and two other people just ran through Ascendant challenge and after dying a few times each, we got to the next part where we ran to get our reward ("toland beckons you"). And whenever we finally got to the part where the chest should be, it wasn't there. I've heard that if someone dies and comes back in, it will despawn the chest and you will not get credit for the challenge. If that's the case... then that truly sucks and I'm out a really good powerful engram :/. Have also heard that you have to carry the sword all the way to the end to get your reward, which would also be stupid since you would have to do the whole challenge solo as running in a party doesn't yield multiple swords to spawn.
No you dont have to carry sword to end and you have 2 min to get to the end for the chest. if you die after 3rd knight dies you loose out though