Is it possible to disconnect the head without the player dying?

You can use humanoid:SetStateEnabled("Dead", false) to prevent a character from dying when their head joint is severed. This will outright prevent them from dying though, so if you don't want that your best bet is to make the head invisible and detach a clone that appears to be the real head in the real head's place. If you want there to be no collision box for the head, you can modify the weld so that it is tucked down into the torso.