I can't imagine why anyone would ever go back in the Sea Org after successfully getting out whether they remained in Scientology or not.
In my brother's case, he aged out of the job market in his particular trade, and was in a terrible financial pickle (of his own making).
When he first left the Sea Org in 1983 (after ten years of service), he was 27 and didn't know 'shit from Shinola' about how to navigate real life. My mom took him in, and I hired him onto my crew at my place of work.
In short order he became my most reliable, hardest working junior, which is kinda par for the course for ex-SO. He learned the trade and went on to excel at it. He wound up staying in that trade for thirty years, while he and his wife raised a family, always working for Scientologist-owned businesses. Sadly, he never strived to learn any other hats in the field. As he grew older, he became less and less desirable as an employee, due to the fact that he only knew how to do one specialized function in the industry, and there were tons of young bucks willing to do his job for much less pay.
Meanwhile, his marriage had fallen apart and he was on his own, trying to re-invent his life as a single man. Just as when he'd left the SO in '83, he found himself cast into a life situation he was totally unprepared to deal with, except this time, I could not help him overcome it. He was locked into a dead end of his own making.
Essentially, he never escaped the mindset that had been imprinted on him during the decade he spent in the Sea Org. During the thirty years he was out, he continued to operate in the same way - like an indentured servant, lashed to the yoke, doggedly grinding away for other masters, who were all too happy to let him slave away in the same labor intensive position, year after year, after year. As with the SO, as soon as he showed a bit of aging, they turned him out to pasture without a thank you or any kind of safety net.
It's just another example of 'the prison of belief' at work. He ran back to the SO out of fear because he just could not unhook himself from the institutional yoke that bound him to that one job. He simply couldn't reach beyond his narrow existence to find different work - and so he failed.
I don't know whether he's considered what will happen to him when the Sea Org no longer finds him useful. He's got to know that the day will come when he's incapable of pulling the long hours and all nighters. I'm sure he's seen old timers off-loaded in their elderly years. Maybe he's under some delusion that there's an old folks home for retired Sea Org vets? I have no idea.