If you transfer 2. What happens if one doesn't make it?

Ive had RPL at 8w and my ivf doctor suggested doing our last 2 the next transfer as we are officially out of funds and do not want to discard my other euploid.

What happens when you transfer two? (I've met many women's with success with twins or both arrested ) but never really heard many stories about if something happens to the one.

I'm wondering if one stuck and the other arrested around 8w or longer? what happens then?