This is what I suggest, as it is what I've decided to do for those of my ancestors I can't find a death date for (records were sketchy back in the 11th century).
I find all the children that they are supposed to be the parent of, or any other record like marriage, occupation, knighthood, and so on. Which ever is the latest date I set as the death date and select Period after. As they must have been alive at that date and died after that date.