Bug with important items missing

Hello!

So i was playing the main story today. I finished act 4 today but ran into a bug.
If i would'nt have missed an important item i would'nt even have posted this.
I killed Tavakai but also died in the second the dialog ran. I thought whatever, i can pick up the items after. Unfortunatly i could'nt pick them up because they despawned for some reason... Now my game is a bit bugged and i missed all the items. Is it possible to reset the boss so that i can defeat him again and hopefully get the item again?


https://imgur.com/a/ommM9xz