The post office or the USPS does eventually recycle and reuse their tracking numbers but only after a year.
So the USPS does keep their tracking numbers for a year and then after a year the tracking number goes back into their system to be eventually reused for someone else's packages.
So the tracking number that you have now may go to someone else eventually after a year has passed but the tracking number is good for your package for up to a year.
Although if you've lost your package and have not found it within a year then it's totally lost anyway.
Sometimes it may take a bit longer than a year for the tracking number to be reused but it does eventually get reused.