Once the biz owners sister "earned" her rapid rise to GM she made it her mission to force me to quit. Passive aggressive, childish, hypocritical and willing to embellish anything that gave a reason to be critical. Even admitted to intentionally not responding to any email from me (lasted nearly 4 months!). I dealt with it for years til finally giving in.

In addition to documenting as much as he can, he should find ways to ask co-workers opinions without being too transparent​ on why, and do so via text or another form that he can easily access since not the companies. Using work email isn't good cuz theyd block access the second hes gone plus its monitored. Having co-workers give their evaluations on performance, change in performance, value, especially any questionable treatment theyve seen by management.

Personally id push hard for the buyout since he just wants to get rest of home paid and thats not enough to keep someone happy for 2yrs in a toxic environment. No reason he should have to take a lot less $ than he'd earn over the next 2yrs though. Could probably get 70-80% of 2yr pay as lump sum by telling them he'll train his replacement for as long as they'd like, and why its really saving the company 20-30% plus all the expenses theyd pay in 2yrs after he leaves to hire/screen/train someone who at best has a tenth of his knowledge and will likely hire multiple people who don't work out before getting the right person