Cardinal's been working with Matt's PI agency, though probably not openly. No congressional medal of honor or span of pardons for him - even if they were offered, he's unrepentent - he's still keeping to the shadows, involved with the underworld and quite probably the Zarek Group, though he became more of an information dealer than a thief. Still, he have helped out and worked with Parkman 'under the table' bringing him information and giving him backup now and again.
Eventually, he just vanished one day. A few people may've seen him since, but only as a shadow, and he's refused to discuss personal things. Maybe he found out something too terrible to deal with. Maybe he took an injury that'd kill him if he changed back, and he's too proud to ask for help. Or maybe his power just evolved to the point that he -couldn't- become flesh and blood anymore.
These days, the only person that sees him regularly is Logan. And he doesn't even know it.