I wouldn't mess around with the one GOOD cylinder if you're running on a budget.... just leave it together.
I would, however, buy a brand new piston and new rings for the DAMAGED cylinder.
For the havoc that a piston can cause if it happens to fly apart in the future, it is not worth trying to use a piston that has been subjected to an impact like that. Pistons endure a lot of different stresses due to heat and speed. My brother had a brand new piston come apart in a freshly rebuilt engine that never saw over 3,500 rpm, and this was a brand-new piston. (He got it shut down in time as soon as he heard the racket going on -and had a long walk home.)
I wouldn't chance using an old piston that has been whacked. Just my opinion.
At any rate, you will be looking at going through the "break-in procedure" to seat the new rings for the one cylinder.
May be a good time to upgrade to HC pistons, but them you'd have to use premium gas. And cough up more cash for the extra parts and labour.
.....What to do, what to do?
Think it through what ever YOU decide is best for YOU and your Roadie, Bro.