When I got to this point I shot to the wall and noticed that i hit something, then I started shooting and "killing" something invisible... when I moved towards the wall on the left the boss conversation started but when the fight started the boss didn't move and his life bar was empty, so I had to kill myself... when I revived the boss was already dead, the thing is... I don't have any new items in my inventory and if he was to give me something, I dont have nor know any way to go back before killing it....

I don't think the face gives you anything except souls if you just mean the miniboss. Only the three main bosses (Gorgons) give key items on defeat.

By the way if you exit the game instead of getting yourself killed you can reload from the last campfire.

yes I was referring to the 2nd main boss and you cannot escape once the fight has started unless you kill yourself, I know I could have just loaded the save, but I saved by mistake right after I was revived, so the boss was already dead and no blue gem was given to me, I just started again and got to the same place in half of the time

According to the l latest patch notes the issue shoud also be fixed now.

Same situation here, Gorgon Volantis is dead, but I have no blue gem, updated to the latest patch. Is there some way to fix this without a complete restart of the game?

love the game though,
greetings& thanks