A few years ago I was diagnosed with trigeminal neuralgia. I don't have it anymore. What are the chances of my tn coming back?

Unpredictable. Some people have an episode of trigeminal neuralgia and never have another. The longer the time between an initial episode and any subsequent one diminishes the likelihood that it will recur. Unfortunately, it is not all that predictable.
Help available. Modern surgical treatments now include needle balloon decompression, and can stop many of these episodes cold. Newer meds far more effective. Unlikely that this problem will re-emerge if you have been symptom-free for several years, but if it does come back, lots of new options.
Depends. It depends on what caused it in the first place. Trigeminal neuralgia just means that there is pain caused by the trigeminal nerve itself misfiring. Usually this is a disease that is not cured, but must be managed chronically; congratulations on you no longer having it!