IMO, he should look for a job, track his spending for awhile, saving as much as he can, and investing as much as he can, especially right now during this market dip. That will let him see his average spending, and see if it's feasible.
Alternatively he could just go for it, and if he ER fails, look for a job then. If he's okay with that possibility, and he doesn't think there will be a significant difference in his ability to find a job now versus after an employment gap, that could be okay.