Anacybele, I'm often okay with Ike/Elincia, too, but you have to realize that there would be little to no reason for Elincia to leave Tellius in pursuit of him, let alone her stepping outside of Crimea. Unless she needed to go to Begnion or to Gallia for whatever future political reason. And at that point, Elincia and Geoffrey would be husband and wife, as much as you'd hate it.
He wasn't seen again on Tellius but he was seen on Archanea, where no one knew his name and the things he had done in the other world. As we know, the bloodline goes on into present day Ylisse. Even in Paris' sidequest, Ike isn't mentioned by name, but by title: "Hero of Blue Flames." Let's be hypothetical and say that If someone descended from the sky or emerged from an other world gate covered in blue fire, gee, wonder where the name was inspired by? Aside from, you know, Yune's blessing.
Maybe Ike did something that still counts as heroic and the name followed him from one continent to another. (And someone correct me on this as I'm not entirely certain.) Isn't the OWG near where Paris' sidequest takes place? Paris would be on Tellius and not Ylisse if he was, in fact, related to Ike and Elincia. Rufure mentions there is a hidden village where Paris is located and I'm willing to bet either it's where he was born, or it's just a favorite place of his to visit as it might be the only place on the whole continent that he considers his real home.