This is an easy fix, the Rally 200 has a chain drive reverse. The chain is a 35HD you can get off Amazon cheap...the factory is over $60 and discontinued. You need the chain a break and rivet tool for chains also. Total price is under $50 to fix.
Base off your year the rear brake is on the transmission 🤮. It a metric 5 or 6 Allen key and 10mm and 13mm and the case comes apart fairly easy. Take it apart carefully so you don't lose parts. Measure and assemble the new chain and install in reverse order. I did my wife's when it failed the second time on the trail (used a standard 35h chain) in about 45 mins.
I would not recommend driving with the chain still in the case. If it gets bumped just right it's game over and tears a hole in the case....mine was scarred pretty bad but wasn't through.