I'm not sure exactly what to think of this myself. I guess it's better that MP leaves than continues with a band that he no longer feels comfortable with, but it's still a shame, especially b/c the band is continuing to grow, both musically and in terms of sales.
As for DT, I can't imagine a parallel situation where a driving force for the band (not the singer) leaves so abruptly. I'm guessing that the closest would be if Lars left Metallica, or if Steve Harris left Iron Maiden. To many, MP was DT. Let's hope that this move transitions the band into a new beginning and does not signal the beginning of the end.