It's possible, yeah
. He would be fine in the original timeline but after Belthesar started fucking with the timeline there's no telling how screwed Robo would be. I think I may have cleared things up with my latest post there though (unless I've hugely overlooked something, you're good at pointing those things out when I can't!).
I think, in light of it, that Robo would still appear in 2300 A.D. in the Ideal Timeline. The major problem with your theory is that there would be no counterpart for him when the dimensions split because he wasn't there. All matter/energy is doubled at the split point, but Robo doesn't exist in the timeline until he reappears in 2300 A.D., so he should be fine. But maybe you can refute me over there.
I anticipate that we will be able to figure out other examples where your puzzle-piece analogy does work. I'm already beginning to think that it may prove that TTI/TB (and DTI/DB) can't be preserved after the reunification point for events that happened only in one dimension but not the other. But my brain is fried so I'll have to work on that later.