Honestly, and I’d been reading this over the years - he seemed to have been thriving (in his own way). forgive the yahoo article:

https://www.yahoo.com/news/the-unabomber-s-not-so-lonely-pri...

guy was extreme end of the loner spectrum, probably into personality disorder range, and didnt mind solitude at all, the lack of freedom was probably what bothered him. he did maintain a ton of correspondence and probably ended up forming more relationships in a supermax than he ever had his entire previous life, by quite a bit.