Hi @DataInspector,
There are no penalties for letting your Part 107 Certification lapse. The Part 107 does not expire, it must be renewed however if you plan to operate your drone for non-recreational applications.
Letting the certification lapse will not prompt you to retake the initial Part 107 exam again. If your certification is not renewed, then you can only operate for recreation until it has been renewed. If you are not using your certification that often, you could let it lapse and then renew once the FAA launches the free online training sometime in March.
The other