Since the leave is unpaid, does it basically just mean your old company has to hire you back in six months if you decide to come back?
I've seen it happen, people take extended leave of absence on FAANG, to pursue some non profit stuff or simply to prevent burnout.
During those, you're still covered by healthcare plan, but everything else freezes: let's say you take 2 months off. Then your RSU that was supposed to vest next month is now vesting in 3 months. Your vacation days don't accrue during those 2 months, etc. Obviously, since you're not getting any salary, there's no contribution to 401k happening during those 2 months.
As the guy who thought he could do better and has to come crawling back, admitting failure... that sounds awfully uncomfortable.