This! FIRE as fast as you can so you’re not at the whim of this class of people (management class, broadly speaking). There is no security, no one is coming to save you except you. I speak from experience.
1. He doesn't have to change his spending habits at all. He just needs to direct the extra income into a saving account, maybe check on it one a month/quarter/year and move it someplace like CDs, Bonds, or ETFs.
2. His goal is to continue to work. Having a healthy savings account can keep you secure while looking for another job.
Relevant recent thread: https://news.ycombinator.com/item?id=35514464
It's a lot more reasonable to have a goal of, say, having 2 years' of life expenses saved up in case you want to take a faux-sabbatical mid-career. If you're in tech in the US, this is really not hard if you aren't spending extremely lavishly.
Personally, I've been in the position for about 5 years now where I could have ended up mostly retiring if that's what was in the cards. And it's a very liberating feeling even if you don't have to or choose not to exercise it. Makes it far more of a non-event (for you personally) when layoffs come knocking.