Edit: kara beat me to it by a few secs, so I'm editing out the first part of the post, dealing with the wrong assumption that BtRL was strictly canon.
As for the TOS galactica - obviously it can't make a comeback as the same class as the Galactica. But if you look better you'll see that every TOS ship that reappeared in TNS was altered at least slightly. The mkI shuttle, the TOS raider we first saw in Razor, the TOS baseship.. all similar but none of them are identical to the TOS versions - some have been altered more, others less. The point is, they used the redesigned TOS ships in a different story - this time they're relics of the first war - as a nod to the first series, as it were. If the TOS Galactica was to make a comeback in Diaspora, it certainly wouldn't be as the Galactica, but maybe the design could be used (maybe altered slightly, if nothing at least the weapons would need to be changed) as a different 1st war class.. as a kind of a homage to the original show.
However right now we don't have any plans regarding this, so arguing whether or not we'll do it is kind of pointless, especially since we don't know yet ourselves.