A situation I have seen that causes immense trouble with wills and estates is where someone is married, the marriage ends, there is no divorce, and then they move in with a new partner and don’t marry.
I can’t give any easy answer as to what this means for how an estate is handled as each situation will be different, but I can tell you that there will be an awful lot of work for lawyers trying to sort everything out. I don’t think the people involved realize how complicated it makes things for their family if they die.
Here is how this can happen: suppose Josie is married to Mike and they have kids. They do wills leaving everything to each other, failing that, their estates will go to their kids. No problem there. Now, if Josie leaves Mike and divorces him, in some jurisdictions there are provisions that would invalidate her bequest to Mike and her will would be divided according to the laws of intestacy. (again, don’t take this as legal advice and speak to your own lawyer because this isn’t how it works everywhere). But if they don’t divorce, the gift to Mike stands. If Josie then moves in with John, she really needs to think about her will, as Mike and the kids are still the ones who would benefit under her will and John would receive nothing, even if they lived together for 20 years. (see also Wills for Second Marriages which cause all kinds of other issues). John would have to sue to try to get anything from Josie’s estate, instead of it going to Mike, which is probably not what Josie would have wanted.
If Josie and John live together for a few years they can be deemed to be spouses under the law and John and Mike (and the kids) would end up having a battle to decide who should inherit and who is the rightful spouse. Josie could be seen to have the obligation to provide for John under her will, even though she has left everything to Mike. She might want nothing further to do with Mike, and this might not be what she would want. She might prefer that everything go to her kids instead, but she needs to be aware that if she and John are in a spousal relationship she has an obligation to make provision for him under her will or else he has the right to make a claim under her estate and battle it out with her executor. If she doesn’t want everything to go to Mike, or for John to have to do battle with Mike, she needs to get her will updated.
I have definitely seen it happen where people simply move on with their lives without realizing the battles they leave behind if they don’t tie up these loose ends.