I suppose I got the coticule too wet and the glue that held it to the slate backer turned loose.

Now I'm debating what exactly to do with it. Options I see:

Glue back as original.
Clean/flatten the blue side and try it out next time i hit a honewall.
Glue it to a board that fits the stone holder (coticule is too short). Or fit it to a board-unglued such that blue can be accessed..
Forget the other side, re-glue to slate, fix the whole shebang to board to fit holder.

What would you do?

Also, is there a preferred adhesive for this work?