nmchigger said:
Father in law recently passed away in MS. spouse is an heir, but has some health problems. What happens if she passes away prior to probate of the estate?
Survivorship rules cover the situation where the heir predeceases the decendent. In this case, the spouse was alive when the FIL died, and has apparently continued to live. If the spouse dies prior to the FIL's probate, the spouse will still get her share of FIL's estate, but then her share will go on to her heirs via her will or intestacy.
The heirs are determined at the time of death, not the time of probate.