I've never had any provinces picked up from dead in-laws, but I have seen AI factions gain them (doh! Not fair!) I believe it depends on your current queen being from a certain faction -- don't think it works if she's just married to a prince, has to be the king (but as it's never worked for me I haven't really tested it
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With regards to re-emergences, I think I read somewhere that it depends on an unmatured heir from the time the faction was eliminated going into limbo until he gets an opportunity... which might explain why some of the "new" kings pop up when they're 60 years old and beyond begeting any heirs.
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