What happens, and what documents will a mortgage loan servicer require when death of a spouse/co-borrower is reported?

Question

Mother died recently. No probate. Father & mother (married) both co-borrowers (father was primary) on principal residence they owned as trustees. 
 
Home is in revocable living trust. Mother & father are the grantors, father is successor trustee. I am sole beneficiary. No one else is involved with trust. Father is now only one on title (as trustee). 
 
Father refied house, and will get check from escrow. Because he didn't report mother's death to servicer, check will be made out to both of them (not as trustees or to trust), and will use "AND", not "OR". 
 
What will happen if my father informs the old servicer, who is about to be paid off with the refi, about my mother's death, so check can be written in his name only? 
 
Is there any danger for him here? Typically, what would they request? Death cert, maybe a trust cert?  
 
Could he cash an AND check as successor trustee? If so, how? He has no trust account, but still has a joint account with my mother (bank isn't aware she passed).

Maurice Mandel II · Answer

So this goes with the other question posted in probate.  Apparently this check comes from an escrow on a refi and is a one time deal. Your other post said there was a joint account.  Deposit the check there.  The old lender is no longer involved once paid off and does not need any additional information once it receives the money.   Or take this whole thing to an estate planning attorney for review- which you should do since one of the trustees/ grantors of the trust has died.  It needs to be evaluated for additional changes, this is a major change in circumstance. 
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Q: What happens, and what documents will a mortgage loan servicer require when death of a spouse/co-borrower is reported?