you're begging the question here,
I don't think so. I'm making an assertion without evidence to back it up, but that's different.
the assumption that tabletop D&D is the trunk of the D&D tree is a genetic fallacy.
? Then what is the trunk?
Looking at the products, everything is based off the RPG. The settings came first as RPG material, and then the other material was based off it, in same cases straight forward translations (like the video game The Template of Elemental Evil.)
Except for the first movie (and possible the second; I haven't seen it.) And one of the big complaints, brand-wise, about the first movie is that it wasn't connected to any of the other stuff that is D&D, which tends to hurt the value of a brand.
Yeah, I don't think so. I've never read an X-Men or a Spider-Man or a Batman comic in my life. You have to realize that hundreds of millions of people watch these movies, yet a really popular comic won't even move 100,000 units.
Were comics once the core? Absolutely. They created the initial awareness on which later products have capitalized. Will that awareness magically disappear if the comics cease to exist? Nope. It's there, and as long as it continues to be cultivated in some form, it's not going anywhere.
Two things. Maybe X-Men can move from comics to movies, but they haven't; the movies are still built off of the events in the comic books. Even so, D&D hasn't come close. If you ask random people about D&D, they'll talk about roleplayers. There's nothing to tie the D&D brand together except the RPG.
Secondly, I don't think the numbers matter that much. What matters is where your creative people are working and where your hardcore fans are. The new ideas for the X-Men are coming out of the comics into the movies and other licensed products, and all the hardcore X-Men fans consider them the base line. Those fans light the fires for the movies.
If the RPG goes under, the D&D brand will have all the respect of Atari; it'll be a name people stick on stuff that has nothing to do with the real Atari back in the day. Maybe if they can fire up the MMORPG, they can make it the new creative base and the new hard-core fan base. Otherwise, it'll mean nothing (just like it did in the first movie) and will quickly die out.