I don't take from the interview that he'd never leave, but I do take from it that he might eventually do so. I think he'll stick around for the next album at least, and probably do the tour after that. But we could be talking at least three more years for that. I think that's what I took from his body language...not that he'll leave right away, but that he'll probably give one more album/tour cycle a shot and then possibly hang it up.
Despite its longevity, DT's lineup has been pretty consistent. Most bands aren't this tight. Yes went through dozens of lineup changes. Genesis went through a bunch of attrition.
I kind of wonder when James might decide he wants to hang it up. I think at some point, he's going to decide, "hey, my voice isn't what it used to be...these things happen when you age as a vocalist." Although TA was probably one of his best works with the band, I think he might decide sometime soon that he doesn't want to do all the touring. DT could get its own version of Jon Davison.
It would suck to see MM leave, and while I get your point on "one more album/tour cycle and then we'll see", I wouldn't be so sure it's going to end up that way. We can't decide how he truly feels or not, but if we can be sure of one thing from this interview, as well as other comments on his fb page, etc, is that he really wants more writing involvement with the band
Now, let's see their inmediate plans: The TA tour ends today, and then they'll have a break untill the last days of January, when the Images, Words & Beyond tour starts. We don't know the setlist yet, but it's going to be mostly stuff from pre-MM DT, even though they will definitely include some ADTOE, DT12 and TA in there. The dates they've announced so far end at the last days of February, which means a full tour month for the band.
After that, they'll either continue that tour on more cities/countries, continue the TA tour on Asia/Australia, etc, or take a couple months off and then start the new album. Those are the 3 possible options I think they have (I doubt they would take a long break after that).
So, depending on how long the touring for next year goes and what plans they have for the future album (remember they tend to start talking about their next album with a lot of anticipation), Mike would have to consider all the options he has. If the band plans to tour for most of 2017 with the IAW thing, he might not be a big fan of the idea, since that would mean 2 full years of touring, he would hate to leave his family for that long time, plus all the effort and sacrifice it takes to complete the tour, whis is, basically, celebrating the old days, not their current music.
If they talk about the new album soon and they (most likely JP) say they want to make it a full band collaboration again, Mike migh give it a shot, because that's basically what he wants. But if their next album plan is more on the side of "Jordan and I will come up with most stuff and you can add your own touch later", that could be a big turning point for Mangini.
In the JMX interviews I've read this year he's seemed to be more excited about the Jelly Jam album and tour than TA, but that may just be him drumming up his side project more, because it's less familiar to people.
It might be reading too much into it, but I remember the time TJJ was touring earlier this year, and they posted lots of pictures, and, every time JM appeared, he was smiling
We all know how Myung, the silent man, basically never appears smiling on any DT photo ever taken. Fans went nuts on their fb page
Not saying he's unhappy with DT or anything like that, just commenting, since you mentioned it