He should have negotiated a positive-to-neutral fact-based reference (good reviews, verification of salary, departure by his volition-- a revision-of-fact but one that companies will usually support) in the severance process. Chances are, he would have gotten it. This would have mitigated the career damage and gotten him a good job much sooner.
Remember that a severance offer is a starting point. If the only thing you want to add in negotiation is something that doesn't cost the company money-- good reference and a revision of the record to say you left voluntarily-- they'll usually give it, unless you did something illegal and they're afraid to give you a good referral for liability reasons.
Getting fired is something that happens to a lot of good people... for all kinds of bizarre and stupid reasons. I wouldn't mention it, as a general policy, but I really doubt that he couldn't find a job because he was fired. He probably became insecure and that did him in. He probably was also too loose-lipped about his feelings toward the previous employer, which is even more damaging because even if a past employer is terrible, one shouldn't let it on in an interview.
"Persona non grata" in the tech community after a job goes bad... that's just bizarre. In my experience, people familiar with startups are the most forgiving of jobs that went bad or ended suddenly, for the obvious reason that a lot of startups fail.
