Tom Williams,
You better come up with %100 of everyone's bitcoins ASAP even if you need to buy them with your own money from one of the exchanges.
Those bitcoins are YOUR responsibility.
I can think of times in my life where I made mistakes, and paid tens of thousands of dollars out of my own pocket to make things right.
Now it is your turn.
Do the right thing.
And you'll do what exactly if he doesn't?... It's all well and good that you paid up when you made mistakes, but assuming others will is a recipe for being taken advantage of.
QFMFT