Without the mask to pump in the venom that his body depends on (in certain stories), Bane would probably lose his immense strength and go into painful withdrawals.
So either Bane is dead, or he’s in a state that wouldn’t make him much of a threat to anyone, super-powered or not.
That said, the fact that this mask is hanging out on a mantle and not on Bane’s face could mean the villain merely “existed” and isn’t currently able to wreak havoc.