Having personally been inside one a few times, replacing the battery is do-able for someone with hobbyist-class skills. Harder to do than an empeg drive replacement, easier to do than an empeg button hack or VFD replacement. It's probably about on par with doing an empeg AC adapter jack replacement

I'm slightly below hobbyist-class with my soldering. I sent my empeg across the pond to have the AC jack replacement done, so I'd probably be sending mine to someone with slightly better skills if this ever became a problem. But this all implies the batteries become available, and only time will tell if that happens.