I have not done this myself, but have read many articles on the subject. From what I gather, it's not 'regrets' people have --- fulltimers, for the most part, go back to a more 'settled' lifestyle after a while.
Apparently, a lot of previous fulltimers missed a routine and seeing the same people, so they settled for an RV park to live in. They just got tired of meeting people, and then they were gone.
Others simply become tired of travel and the wanderlust leaves.
Then, there are some complaints that if something is wrong with your RV, and it needs a repair, you have no house until the repair is completed.
But again, the articles I have read don't talk about regret. Just simply that after so many years, people choose a more settled lifestyle. No problem with that..