Is it normal that seller stays in the house after the short sale deal is closed?

[HUA YANG]

We were waiting to buy a short sale. The bank finally approved the price but requires 30 days to close the deal before going to foreclosure, which will be before the Christmas. However, the list agent states that the seller does not move out of the house until three months later by next March. Our agent indicated that we may be able to give the seller some credit like three months rental, $6k -$10k, to persuade him. My questions is:
Is it normal that the seller to stay in the house for a few months after the escort is finished? Our concern is we may be facing the problem to pay the mortgage for someone else to live in the house. I guess the bank and all realtors will walk away after the deal is closed. I am afraid it would become a problem between the seller and us. Then we have to go to court. I do not want to see that happens.

Any advice would be greatly appreciated. Thanks and Happy Thanksgiving to everyone!