What JB said. If you're not happy with your lawyer, get new one.

But statute of limitations (such as the stale complaint rule) generally do not require the agency in question to grant you a "clean bill of health". It's probably legal for them to keep the case in limbo for for an extended period, although the longer it drags out the lower the odds that they'll ever be able to make it stick unless they have a good reason for the delay.

They know that an open, unresolved issue like this can be very problematic for a professional pilot, so they might be stalling deliberately to punish you or coerce you to go along with their plea deal.

You might investigate whether or not the rules or FAA internal policy require any sort of formal closure of an unresolved case, and whether you could FOIA the info about the case.