Well if the tempo did take effect(which one could rule it didn't as the character is still technically a technomancer, albeit a latent one, but that's a GM call, not RAW) then that would kill any future chance for virtual kinetic abilities as, once a specific ability has been expressed, it's corollary is prohibited.
I'm not sure how a character loses his Magic score from tempo without becoming addicted and without being considered a burnout.
I don't think anyone is implying that possesing spirits can't do what they do because the vessel is a TM. Just as spells affect TMs, I would imagine possession powers without inducing magic do to.
However, I can't see a scenario where someone is a mage, loses their powers and then gets to become a technomancer.