It depends on the return policy that with your sale you did. If it was still within the refund time at the time of the complaint then he has to send it back and then you should refund. You should contact ebay about this question because they have several policies regarding this type of transaction.
No they cannot file a criminal case against you. The worst they can do is file a complaint with pay pal and the worse they can do after trying to mediate is to refund the buyers money. Good Luck.
