a buddy of mine had been an EMT for years, and once he was hired as a cop, he decided to let his EMT lapse. the DOH actually investigated a complaint that was filed against him, and he simply ignored their requests. His thinking was, "I don't need my EMT for my job, have no plans on keeping it up, so what's the worst they can do? take away my EMT that I have no intention of ever using?" In fact, the only reason he actually complied with the investigation was because they contacted his new employer, who ordered him to go down (on company time) and assist with the investigation.
So if you have 0 plans of ever doing anything in EMS ever in the future, or anything that would require you to be an EMT, ever again, let it lapse.
I recently let my NJ EMT lapse (after having it for 15 or so years)..... but I also have 0 plans that would require me to be a NJ EMT since I moved to NC. But if there is a chance you might need it in the future, than I would keep it up, provided it doesn't interfere with your current full time job. It's much easier to keep it than to get it once it's expired.