Last boss bugged ??

Hi!

This is my first character, first run of PoE2.
When I flighted the las boss on Act 3 it killed me only to die himself due to some grenades on the ground.
When I respawn the boss is dead, the loot is not there and the final scene is over.... I don't know what I have missed.

I am now forced to go to the Cruel campaign... if I start the map again I am back to cruel every time I use a portal... what can I do?