OP- lots of good advice and a tough lessons learnt in hindsight, not that I expect that there will be a next time.
In the cold light of day, what is the extent of the damage and costs to put right? Is the shifter and frame still usable? Can they be tidied up along with some new bar tape? I’d take your bike to a trusted LBS and get their opinion.
If the event was part or fully sanctioned by your work, I’d speak with your boss and see what they can do to sort you out, after providing a favour to a “colleague”.
Presumably the borrower has shown no cockwomble tendencies previously, or you would not have lent to him? He has certainly demonstrated this now to you, his colleagues and manager, so I would not worry too much about him not speaking to you. His cards are marked and maybe he doesn’t care (sounds like it), but no one at work will ever do him a favour again.
A payment plan, would you ever see it? Life’s too short. Tell him what you think, the damage he has cost and shut him out. Karma will catch up with him soon and possibly some bombers too. Does he ever remove his shoes at work? 🙂