Just how much damage did he do? Let his work guide you on how to re-profile the handle, and if necessary, the blade.
My dogs have never gotten to an Opinel, but they have buggered a couple of Moras, both of which are still in use. On the wood-handled 612, I used a length ov bicycle inner tube to cover up the tooth marks. On the Companion, I just de-burred the gouges with another knife, and kept on using it.
Edit: just reread your first post, so it looks as if reprofiling the handle is a non-starter. So here’s another thought, depending on how much of the handle remains, no matter how shredded. Perhaps you could use the fibrous mass as a matrix for an epoxy filler like Marine-Tex (sp?). I have seen some seriously dry-rotted brightwork salvaged to the point of utility with this stuff.
Or, pack some Sugru into the shredded mess and make yourself a new handle that way.