I worked for a shady evil company, and when they illegally fired me, I never ended up returning a laptop - thinkpad running windoze.
Let’s say I wanted to put Win 8 or similar on it so I can play some video games. What would potentially be barriers to doing this? Said evil company is hopefully going out of business soon, and is a clusterfuck anyway, so they might not end up asking for it back.
If OP got his last paycheck, done deal. Yes, he surely signed for it, but no laptop is worth the legal cost of a lawsuit.
SOURCE: Issued hundreds of laptops, of all varieties and prices, for multiple companies.