In Felltower, I fold together some of the options from DF 9 Summoners, and most of the perks, etc. of Necromancers, into the Wizard template options. Basically I like the idea of Summoners and Necromancers, but I prefer them to be types of Wizards instead of their own templates.
Because of that, perks like Lesser Lichdom* are more widely available.
The perk is pretty specific - healing won't save you. You're already dead. I suppose if someone had a 300-carat gem spellstone of Resurrection I'd allow for that to work.**
The question is, what about wishes?
I've been known to pass out rings with wishes in them. Old school, ask-and-get one-second time to use wishes.
What if someone dies, has Lesser Lichdom, and uses a wish to undo the effects of dying?
On one level, it bothers me. It's a 1-point perk meant to get you 2-7 seconds of pre-death vengeance. If said vengeance (or running out of a trapped area, or stepping into a gate, or whatever) makes it easier for you to be brought back with Resurrection, fine. It's a valid use.
But having some extra time to get out of dying in the first place seems a bit . . . disappointing. It's not really the spirit of the "my goodness, he's still coming" or "I'll get you back for killing me" intent of the perk.
On the other hand, it's a wish. I don't hand them out like candy. You can't get them easily. They have great effects.
I think I'd allow a person operating in that limited window to use a Wish. You'd have to word it properly, but you could even undo that death check. It's no more or less than using a wish as an ersatz Resurrection anyway.
I'd be less generous in allow a broad-scale "I wish we were all safe and also I wasn't dying" or "I wish we were all healed fully" type wishes, though. You're dead. It's going to take a good chunk of what a wish can do - maybe all of it - to fit that. And wishes that ask for too much don't always take effect at all.
* And its Barbarian equivalent, Not Done Killing (Barbarians, p. 18)
** But they won't. They just won't.