Logan was nearly impossible to kill for regular humans with conventional weapons. Nagash could age him faster than he could Regen. Gelt could rip out his skeleton. Teclis could vaporize him. A Vampire could make him thier Thrall. Logan has no Magic Resistance, physically he would win most fights, even giving Grimgor a run for his Teef.

Could you imagine a WW1 soldier seeing Logan Regen and telling people about it? Everyone would think the soldier went crazy. If a State Trooper reported Logan's Regen then Witch Hunters would be inbound with a passion.

Adamantium is adamantium not lead. Logan does have basic mental defense from his "primal mind" which lets him fight off telepathy.

Even if Adamantium was resistant to warp energy then only his skeleton would survive a warp blast and Logan would still be dead.

Logan has regenerated from just his skeleton once.

Because his brain was still intact. Decapitation and brain destruction is how you kill him and if you fry all organic matter on him at once he will be dead. Also if magic was used to somehow disable his regeneration then Logan would die of metal poisoning from his skeleton.

Yes.

But are there spells that can negate healing factors? Maybe I've heard of at least one somewhere.

It's magic you can do anything.