The scenario:
Should IP Info still provide information about this temporary user (to those with the relevant user right)?
Thanks are due to @Tigerzeng for raising this point on Meta-Wiki.
Per T318462: IP Info shouldn't be aware of revision if user doesn't have access to it, IP info is only available if the user has access to the revision.
As a sysop on zhwiki, I can't access IP info if all the contributions from that particular IP were deleted. By "deleted", I mean that Special:Contributions shows nothing but Special:DeletedContributions shows the page they once created. I did have access to its IP info but lost access to it right after I deleted the page. I am able to see the revisions of that deleted page and thus "have access to the revision". Not sure if this case was covered by T318462.
For deleted edits, the IP information should available on Special:DeletedContributions instead of Special:Contributions. See T318463: IP Info accordion should show up on the Special:DeletedContributions.