Every state certification commission is different, some make allowances for an officer who is not working and some do not. Some may toll your certification while others require you to keep current while not working. I recommend that you read and fully understand your state P.O.S.T. or certification commission's rules.
If you're working and your municipality is facing financial distress, do your research. If you're in a union state, contact your union regarding your rights. Each state has different rules. Do not call me; go to their website for answers.
Within your state, you may work for a county, city, borough, township, village, hamlet, school district or regional configuration. Each has its own rules or civil service rules. Do your homework here as well. Do they have mandated retirements for those who have reached the retirement qualifications? What is the code that gives them the authority to furlough the last hired?
Make sure you understand re-employment rights. Once you are in a position to be rehire, you'll want your opportunity. These rules should be clear for you to understand, if you have rights to be brought back. If you have questions, speak to your human resources contact and your union representative (if you have one). If you are a union representative, don't wait for this to happen to your members.
Follow what's going on with your employer. Maybe you don't live in the municipality, so you haven't been paying attention. Start paying attention, when the words "budget shortfalls" and "layoffs" come over the news, sit up and pay attention. You may be forced to make some tough decisions. If you're not on the job and starting to make applications, research the financial stability of the agency where you're applying. You may need to rethink this application.