The Molten Vault "Animation to the Boss Arena"

In the Molten Vault area, there is a boss "Mektul, the Forgemaster". There is a special animation to enter the Boss Arena where an elevator takes you down there, but my issue is that when someone with a character like mine that does elemental damage, manage to kill the boss due to residual elemental ailments, even after my own death, I am taken to the checkpoint and can't re-enter the boss arena since the elevator animation seem to be a one-time thing, if you kill him since his quest item is on the floor, and it seem to have no other way to get down there.

I had to remake a new instance and run through the map in hopes to fight him again, in-order to get the quest item, and possible access the other area of the map. Now if the first time I've killed him and he dropped a unique which I've rarely ever see even at lvl 42 or valuable gear progression, that I couldn't receive, it would have ruined my whole night.

Also for another player, if he was a real difficult fight for them, and the same thing happened to them, just the thought of re-living the nightmare of fun.

Make so that even if he is killed and his item drops, as long as you're by his checkpoint, that you're still able to enter his arena.