Where do they keep you skull flap after craniotomy?

My brother had an emergency craniotomy almost 2 months ago.

Today he had a surgery to close up his skull, and I was under the impression they would be using a metal plate to fill the gap, but I guess they used his own skull piece, that they had removed in early march.

My question is, how did they store it for almost two months, and what state is it in when they put it back in? Is it still 'alive' or like what do they do to it??

I'm just a sibling so I don't get to speak to the medical team directly, and I don't want to torture him or .y family with my morbid curiosities at this time.