Buyer Dies after Closing

If you mean the buyer dropped dead just after the sale was settled and the deed handed over, it seems to me the buyer was the owner of the property, and from that moment on, the estate is.  But of course I am not a lawyer.  Where a new mortgage is involved, there is usually a three-day right of recission so perhaps the estate could invoke that.  I never heard that a check could be voided just because the signer had later died.  I give up -- I am simply not qualified to give an opinion on this one.  If someone wanted to somehow undo the purchase, their best bet would be to consult their own attorney.