Joint tenancy and one takes mortgage

My client and her father were deeded a home as joint tenants. A few years later, the father took a mortgage on the property. Under title theory this terminates the joint tenancy, correct? Well now the father is dying and my client wishes to remain in the home, but to do that would need to modify the mortgage and lower the payments. Do I have leverage w the bank here under a theory that if they foreclose on their half of the property, no one is likely to buy half of a lived in property, and thus my client could likely buy it back at foreclosure for even less?