What happens when interrupting a zip -erm process?
Am I left with something that could be continued where it left off


No. If you send a an Interrupt Unix Signal to zip using Control-C, you'll terminate the zip process and when you run it again it will start from the beginning, overwriting anything it already extracted.

If you instead send a Stop signal Control-Z, the zip process will be paused, and you can resume it later using the fg command.

Note that this will only work if you can maintain the state of your system. That is, if you sleep the system you'll be OK, but if you shutdown, then zip will still be killed. Also, it assumes that the file zip was working with remains available while it is stopped; that is, if it resides ona  network share which you dismount, sending a SIGSTOP will still not work.