When a woman gets married, she takes on her husband's customs. Thus, an Ashkenazi woman marrying a Sfardi man gets to eat rice on Pesach (and vice versa).
But what happens if she gets divorced, or if her husband dies? Does she continue to follow his customs, or does she revert to her maiden family's?
Does it make a difference if she has kids or not? (I know it does with regards to a Kohein's ex-wife or widow eating trumah.)
I would assume that practical considerations will govern many people's decisions. (E.g. if there are young kids around and she doesn't want to confuse them.)
In theory, though, Rabbi Moshe Feinstein's opinion was that when a woman gets married, she changes her customs because it's logically equivalent to the Polish Jew 300 years ago who finds himself magically transported to Yemen for life -- the halacha is that he should change his customs to that of his surrounding environment. Thus, upon marrying into Mister Goldstein's house, you've moved to GoldsteinLand and should follow the local customs.
It would follow that if Mister Goldstein is gone, it's no longer GoldsteinLand and you would certainly be entitled (though I suspect not obligated) to switch back if you so chose.
