Well, he's obviously happier in Blackmore's Night- their music isn't to my taste (way too twee, based on what I've heard- makes Amazing Blondel seem like Black Sabbath) but I don't think you're ever going to see him do the rock star thing again and really, why should he? He's done that and I get the impression he's never liked it all that much. Apparently, his fave singer in Rainbow was Joe Lynn Turner (who these days seems to be involved in every power metal concept album going!!), so if they reformed it'll probably use him and I don't really want to hear that much. Dio said he'd be up for singing with Blackmore again and always seems to have a lot of respect for Ritchie, but I can't see that happening either, as Dio has committed to that 'Heaven And Hell'/Black Sabbath reformation recently.
I think Deep Purple are doing fine without him. If he rejoined, it would be another pantomime farce and doubtless, a substandard studio album would come out of it, which would be a shame as I think the band have regained momentum now.