He keeps what they gave him, they keep what they get from what he gave them.
Ideally they over collateralize. So if SOL is 100 USDT, he puts in 5 SOL and gets 50 USDT per SOL (250 USDT). If SOL approaches 50 USDT, (say 51 USDT) they sell the SOL he gave them and keep the proceeds (they have 255 USDT and are ahead by 5 USDT). The loan has reached an end condition.
Another thing that could happen is he does something with the 250 USDT loaned to him and he gets 300 USDT. He gives back the 250 USDT and gets back his 5 SOL and now has 5 SOL and 50 USDT (minus some small interest or fee). This is another end condition.
All works on the small scale. But presumably you can think of exploits on the large scale.
A simple one is that the loan is so large in that they can't liquidate without slippage (price moving as they sell causing them to gain less than they anticipated). In this case, they might want to exit a little earlier.