I'm planning a lich as a BBEG villain in an upcoming adventure. I want it to be possible for the party to find the phylactery before facing the lich, as well as discovering how to destroy it.
If they manage to learn where it is and how to destroy it, and do so before facing the lich, would destroying the phylactery also destroy the lich outright, or would it simply prevent rejuvenation (meaning when they do go fight the lich, then assuming they manage to slay it, it stays dead for good)?
The only thing I've found on this site (and I don't trust other sites) is this answer to a question about liches and phylacteries, which says:
The lich does not die immediately, but it is then without a phylactery. This means the lich will not rejuvenate.
However, there's no citation for this. The lich entry in the Monster Manual doesn't seem to describe what happens in this situation (meaning, does the lich die instantly or not), so is there any other information about liches (ideally D&D 5e, but previous editions of D&D are acceptable as well) that describes what happens in this scenario?