I think he probably regrets leaving. To me, it just seems like for him it is quantity over quality. Not saying his projects aren't quality, but it's rarely what he talks about. It's always how many bands he is in or how many albums he has done. That seems to be very important to him judging by his comments.
My personal belief is Mike Portnoy regretted leaving Dream Theater the moment he said he was done with them. He's been scrambling from project to project since then, and I am sure he enjoys his work. But he tried to get back (if I remember correctly) more than once, and he's said how DT was his "baby" so many times over the years, it's pretty damn obvious he knows he screwed up. And he probably also knows he's got almost no shot of ever returning, and it eats at him, daily, as nothing he has done since then has any shot in hell of ever being as successful as Dream Theater.
To be quite honest, as sensitive as Mike is, that has to hurt -- A LOT. He most likely has to hustle and work a TON more than he used to, in order to keep some semblance of the same income level. Whereas he watches the DT guys, who work out of the want to work outside of DT -- they likely don't have to if they don't want to. And that likely gets MP mad, jealous, sad, and spiteful, all at the same time.
Honestly, MP brought this on himself, so it is tough to feel bad for him, particularly the way he has carried himself. But a part of me still does feel bad. He made a grave mistake, one that he'll never get over, and he watches something he helped build (much more than the drumming and lyric writing) thrive, while he's jumping from thing to thing and working like a dog to keep the lifestyle he had prior to the split. And he's not getting any younger. The mega touring and being on the road with a gazillion projects can only go on for so long.
MP had the absolute perfect scenario, and then he made the mistake of thinking he was more important than he really was, and gambled. He lost. And no matter how hard he works, he'll never attain the status that he had with Dream Theater.
The romantic in me wants a reconciliation between all of them. But Dream Theater (and their mgmt, I am sure) know that they are doing great without MP, and introducing a wild card back into the mix, with that personality, is a risk that isn't worth taking, given their success. They don't need Mike Portnoy. But sadly, Mike Portnoy needs them (to feel complete, for lack of a better way to express it), and it is too late. And he doesn't make it easier with screw-ups like this interview.
