After activating the device encryption on my S2 running CM 10.2 nightly, my CDMA radio stopped working
Cyanogenmod nightly builds are development snapshots. Anything can be broken in them from one night to the next. You shouldn't try to use a nightly for your "everyday" phone as problems like the one you describe are common.

Report the bug to the developers and switch to a stable release (or, if you're feeling brave) a release candidate or milestone release.