His option is to miss out on features and functionality while essentially ruining his device's security, or to upgrade to 9.3. Selling the watch and buying another is an option as well, but there's no guarantee that a new watch will have an older version of WatchOS on it.
That being said, my stainless model that I picked up a bit over a week ago was running 1.0.1, so it's not super likely that a new watch (unless it's one of the new combos) will be running a newer version.
Personally, I'd suggest he update, lose the jailbreak and the security holes it brings, and enjoy a functional watch again. I'm sure I'm not the only one that wouldn't risk my passwords as well as Apple Pay info on a device that's jailbroken - especially with the shady sources jailbreaks come from lately.