It all depends upon what the Executor of the Will wants to do or the Administrator of his estate chooses to do. It will also depend upon how much equity or value he has in the house after the mortgage is deducted from its overall value. If there is no value in the house because the mortgage is too big, then the bank could take the house back and the estate may not owe anything. Or if there's a much bigger mortgage than the value of the house, the bank could seek to enforce its loan against the rest of your Dad's estate holdings.
Either way, its best to hire a lawyer to handle the estate and consult with him/her about the matter and find out the best way to handle the entire matter.
As a general rule, the lender will only repossess if the mortgage payments aren't made. There is a federal law, called the Garn St. Germain Act, which requires the lender to permit close family members to take over the loan for a deceased person. But the payments still need to be made.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.