So I get this right:

They were using Blockstream green WITH cobovault as the key? Because in that case I would try a fresh Green wallet restore on a different device first with the cobovault. Basically same setup as they did the first time to see if it comes back.

Or are you meaning one had a problem with Green and the other had a problem with Cobovault? Also how did they lose their setup or disconnect the wallet? Any details on what happened exactly? Might help figure out the process to bring it back.