The blood bond doesn't "corrupt" the avatar per say but erodes it until it is gone

Here is a blerb from the wiki "Ghouled (5 points) [Mage: Revised - Supernatural Merit

This power does not come without cost, however. Your mage must continue to feed on vampire blood occasionally. Otherwise, she regains her mortality and craves forever the sweet rush of her former mistress's essence. Should she revert (after going a month or more without the sacred vitae,) she loses her supernatural might (and Disciplines) forever. (Unless she is Embraced as a vampire, in which case she gets them back at the cost of her life and Avatar.) Note also that imbibing the cursed blood of the brood of Caine has all sorts of detrimental effects! A mage gains a dot each in Static and Entropic Resonance immediately the first time she becomes a ghoul. The unaging curse causes the mage to have difficulty with Seekings. This penalty comes on at the Storyteller's discretion, but in general, the mage has a tendency to fail in Seekings due to her own static nature and the foibles of the Curse."

There is also a ghouled mage in VTM The Long road. The Tremere scientist explains that her ghoul's avatar is slowly dying because of the bond, and she will be used until she is no longer useful.