I got the button after completing the very first brain from the general.
After wandering around a bit with the button in my hand I died (damn bear) and left the game.
Today I picked it up again, loaded, and now the button is gone!
I've looked everywhere for it but cannot seem to find it
Can anyone please help me?

Did you check in your inventory?

Or if it's not there, just restart, your not really that far.

There shouldn't BE any bears yet...

How could one kill you?

Anyway, yes, check inventory.

It sounds as if you're towards the beginning of the game. If you carry enough items, you sometimes have two pages of inventory. Check both pages.

When did you last save? You may need to get the button from Sasha again. If not, I dunno...start over. This game is full of glitches but usually they resolve themselves once you reload.