When he hears about the harassment of the grogs by animals, Talus will take the opportunity to invisibly watch some of the grogs who work near the animals to see if he can spy some of what's happening. I'm assuming as one of the newest members of the covenant, it isn't his job to monitor the vis. So he'll probably be unaware of the loss unless someone tells him about it.
I assume that the vis was being stored somewhere secure inside the magic aura. Probably a stone room with a solid wooden door near where the labs are/will be.