Mentors usually transcend a single role at a single company. If your mentorship ended when they left the company, it wasn't mentorship, it was training.
I think that bar is too high and you can still call this mentorship. It would be exceedingly rare to find someone who is going to mentor someone for free across multiple companies. When I mentor vs. train, I care a bit more, follow up more, the scope is broader, more personal, etc., but I'm not adopting you for life.
