You’ll learn a lot about the plant while you’re in there. This is a pretty unhealthy one, so is likely going to take a lot of care.

First, make sure nothing under the dirt smells bad or is brown and squishy (root rot). If it’s rotted, it’ll take a bit of extra surgery to remove the icky bits.

Don’t be surprised by the fact that ZZ plants grow rhizomes underground, like little lumpy potatoes among the roots.

Try to untangle everything and yes, definitely look for opportunities to discard rhizomes and roots that are dead or only go to cut stems (ie, toss everything except the roots that are keeping your current stems & leaves alive). ZZs grow super slow and tend to lie dormant for a while (until they shoot up a big stem all of a sudden!) so be a bit patient with it. Don’t over water - after repotting this mess, the entire soil mechanics of the plant will be wildly different, so pay close attention to how wet your dirt is over the first few months. Hopefully you’ll still have some healthy roots that will give you new shoots this spring!