Your idiocy is boundless. Do you realize that in a later volume, Darsh has a giant airship crash ontop of him and the only thing it did to him was break him into a hundred chibified versions of himself? +1 Luche, and then he reformed himself. You continue to use this lame PIS stuff from the earliest parts of the manga when Darsh was just screwing around with Gara.
And what you don't seem to understand, soldier, is that the Room of Spirit and Time (aka Hyper-Bolic Time Chamber, or HBTC) was connected to the Earth in Kami's Lookout via a Door, linking the two dimensions together. Thus, even when the door itself was destroyed, it would not be difficult to have mad a re-connection between those two dimensions, which is all that Buu and SS3 Gotenks, did; Buu being Mystical in nature and the Fusion Technique being, in and of itself, mystical. You should know that creating links and portals between dimensions is so pitifully simple that you can't even call what Buu and SS3 Gotenks did a feat. Damn near every magic user in fiction can pull that shit off and Krasus in Warcraft created a portal into a pocket-universe where time virtually stands still.
Darsh, being nearly magic incarnate, has spells that screw around with space, realtiy and dimensions. One spell is insta-rapeass ticket to Hell. Your argument holds no merit whatsoever. Just because SS3 Gotenks did something, doesn't make Vegeto/Gogeta capable of it by default. I've seen Shin and Piccolo create matter from thin-air, that doesn't mean everyone can do it.