Yes, the home seller who refuses to vacate should face criminal charges. From my point of view, a sale is a transfer of ownership, which means that once the house's sale is finalized, the previous owner is a trespasser. There's also the matter of fraud, since the previous owner presumably accepted a large amount of money for the transaction and has refused to honor his end of the transaction by releasing the property. Under the circumstances, it would be hard to believe that the seller has any legal standing to stay.
If this seller sold the house and then will not move out then they should be forced to move out. Unless you have set up a living arrangement agreement with the new owners then you have no business being in that house after it is sold. Sometimes you just have to let go.
Once the house was sold, closed on and papers were drawn up the previous owner has no right to continue living on the property. He is being hostile and uncooperative and should absolutely face criminal charges. He was not forced to sell his house, everything was done legally and correctly. He needs to either leave or face criminal charges.
Where in the world can you sell a house, take the money and keep living in the home. I don't know if the owner is mentally ill and having a breakdown but either way he has to leave. If he refuses, he should be removed forcibly. He no longer has the right to live in a home belonging to someone else. Get him to a hospital if he needs help and/or charge him with fraud and theft and unlawful possession.