It's pretty hard to lose P Mod status for inactivity. I recall that you only have to log in once every 3 months, which isn't bad at all. In terms of being able to re-obtain it, I mean my friend did (not a P-Mod anymore), but his friends trolled him apparently, and reported him for something he said in-game (basically reported him for offensive language, which is a dick move, but that's what I re-call), and it ended up getting removed, but he eventually got it back. It really depends on the circumstances behind how you lost it. If you have friends that are currently P Mods / J Mods, then it's easier to get back as they can obviously help bring you back / recommend you (via connections through P Mod forum discussions + P Mod / J Mod Discord), but if you don't, then I'd imagine it would be near impossible.