So yea, this is a rather stupid case and I can kind of understand if I won't be able to play or have to re-purchase my old Uplay games.
That being said, I can definetley prove the games are still in my library. Some time ago I made a uplay account but then did not use it for a while so I forgot both password and username. Then I recently bought another Ubisoft game through Steam (For Honor) and made a completley new account, linked to a different email too for that matter. I don't know why, probably because sometimes I'm just an impulsive idiot, but I deleted my old email before making the new one. So there is clearly no way to recover the old Uplay account. Can I somehow get my old games back, they are still in my steam library after all?
Or is it somehow possible to recover my uplay account by providing all the keys for the games that should be on that account?
So if you linked Steam to another Uplay account, what does it say when you start a game and log into the current Uplay account? It says that the game is linked to another Uplay account?
if that's the case, I don't think there's anything you can do but recover the lost account.
Open a ticket to Support https://support.ubi.com and tell them your issue. Give them all possible information about your lost account. The e-mail you had, the games you had, the linked Steam account, your country, your IP.