In a non-shared services environment, a second personal portal  will be
created. In a shared services environment, you'll be re-directed to the
first personal portal that was created.

You mean services shared between the two portals? I believe these two to be exclusively operating.

If by “exclusively operating” you mean non-shared services, then your answer is that each portal  will have the capacity to have My Sites (a.k.a. personal portals) associated with each portal, so in your scenario, your users will end up with multiple  personal portals. No dissociation will occur.