So my original plan was he'd retreat to a little wizard tower and the tower would literally seep bad vibes due to his mental breakdown. In which case it would not be a secret! And potentially Gale's pursuit of knowledge and magical experimentation might make him of interest to Crane too, generally? So a chance to nose around his tower!

Edit: For clarity, the vibes will make it clear something is going on. But he'll still be masking personally and using illusion magic. In case that was a muddle! He'll be pretending, but the tower will be giving off weird vibes anyway.

But yea, you can Bully Gale into mass murder and then into accepting he's gotta stay because he sucks without you so this is small in comparison.