I hope the decision works out for him. Six months salary is really only a big bag of cash if 1) you have a decent salary, and 2) you can be confident of landing a job of equal or better salary within the six-month window. Otherwise you're just going to burn through it. Given the way hiring has been in the tech world of late, it's easy to imagine it taking six months or more to get a decent job -- you can easily spend several months interviewing to have a role disappear.

FWIW I'd have to be pretty pissed and/or have no confidence in the direction of the company & its leadership and/or have another job/work lined up already to jump ship on a few days' notice like that.