Hi and welcome,
I don't know a lot about TM spinal cord lesions to say if it's normal for TM lesions to disappear or not, i've heard of other TM patients where it's happened and their new neurologist disbelieves they ever had TM until they see their MRI evidence, and I have read a couple of medical papers documenting this too, which suggests to me that it happens but it's not common for spinal cord lesions to completely disappear.
From my understanding MS brain lesions are known to develop, shrink, get bigger, fully recover and disappear on subsequent MRI's but MS spinal cord lesions on the other hand are more static, once they develop and appear on an MRI they are usually seen on subsequent MRI's with additional cord lesions at time showing up too.
MS spinal cord lesions can be hard to pick up on lower strength MRI's because they can be very small, eg patient with objective clinical signs of spinal cord damage on a 1.5T or less may show zero cord lesions but on a 3T or greater multiple cord lesions are visible. TM spinal cord lesions on the other hand are diagnostically notably different because of their much large size/shape more occurring across one or more spinal segment(s)..
Approximately a third fully recover from TM with minor or no lasting problems, but whether that includes cord lesions disappearing from their MRI's i honestly couldn't say sorry....
I hope that helps.....JJ