Oh, there are usually ways to dig the firmware back out, first deencapsulate the die, then use hydrofloric acid to remove the passivation layer followed by using a micropositioner and either e beam or sneak up on the relevant cell from the back with laser ablation.
Secure chips are an arms race, and neiter the pics or the smaller arms are particularly designed as really hardened targets.
All that said, it is usually an order of magnitude or so easier and cheaper to write your own firmware rather then hiring the very specialist reversing skills required.
Regards, Dan.