I let both my group ex and trainer certifications lapse when I took time off when my kids were little. When I decided to go back to work I had to retake the group ex certification. I have not done the trainer one as I felt I am unlikely to make enough working part time to justify paying for CECs and so on for both, but I would have to do that if I wanted to recertify.
There is always a calculus to this: how much will one pay doing CECs and paying yearly renewals while not working versus how much one pays to go do the exam again. I think it depends on how long one needs to be off. And of course one doesn’t always know.
The good thing is that if you have only been off for a couple of years you may not need to buy a bundle with all the study materials, but just the exam, which will be a bit less.
Karin is right, contacting the very helpful people at ACE support is the best way to look at your options.