I am so sorry for your loss.  First you have to know that most mortgages are no longer assumable.  That was for mortgages from a really long time ago. But in answer to your question here no, they can not call in the mortgage.  There are certain exceptions under the law to the acceleration clause - which makes a mortgage due and owing - and your situation is one of them.  So no, they can not call in the mortgage so long as you are making regular and on time payments.  Good luck.