What if Ray had been transported to an alternate universe and not Darkfire?
I'm presuming you mean that Ray went to Dark's home dimension. Leaving aside the how – there's lots of ways that could happen during Paragon City at that time – Ray's first problem is that he's the duplicate. He doesn't have his family or friends to fall back on, and he looks a lot like the painkiller-addicted half-blaster half-defender currently with the J-Stars in Philadelphia. (He also has to deal with a society that expects men to wear makeup, but that's really the least of his worries.)
Ray wants to go home, but Dark's dimension doesn't have portals or Portal Corp or any aliens at all, much less the Rikti War, or even Lord Nemesis. There don't appear to be any magic-based portals, either. Other dimensions, and time travel, are the stuff of science fiction. Since Ray has no idea how to build a portal of his own, he's probably stuck. (Those of you who read Darkfire's origin story will remember that Dark ended up in Ray's dimension entirely by accident; his family, back home, believes he was vaporized.)
Ray will come to the attention of the J-Stars very quickly, because of his distinctive look. Since they know for a fact there weren't twins at Dark's birth, they now have to explain Ray. Ray's a little shocked at his counterpart here, as compared to Ray, Dark is shorter, skinnier or at least in worse physical shape, more bad-tempered, and of course has more empathic powers, fewer fire powers, and no lightning at all. And he wears makeup, glasses and a goatee.
Ray's next job is to convince the Jeffries clan that he's genuinely from another dimension, not delusional. They're able to confirm this scientifically, too. A controversy erupts over the knowledge that there are other worlds out there, copycat worlds. Granted, the copycat world (Ray's) seems to be worse off, with more villains and even an alien invasion. But the simple possibility that the other world exists is enough to have world-changing consequences, as various governments race to create ways of contacting these other dimensions.
Darkfire (who is also called Ray in his home dimension; I'm calling him Dark here to keep them separate) is less than thrilled by all this. He can see Ray, who is what Dark should've been, except Dark's family tried to turn him into a defender. In the process, he was stunted physically, and he turned to drugs for pain relief from the treatments. Dark's resentment toward his family burns brighter: if they had left well enough alone, he could've been Ray.
For the Jeffries clan in general, Ray is not considered a son or relative, as they don't really know him, and his life experiences are different than theirs. (Obviously, Darkfire didn't leave his family in Philadelphia to run his own supergroup in Paragon City, Rhode Island.)
Ray becomes very sought-after for whatever information he can give about portal creation, and of course information about his home dimension. Ray knows he can't stop this dimension from making contact at this point, though he wishes he'd handled it better. All kinds of people begin clamoring for access to the "new dimension": those who have lost loved ones, who want to meet their other selves, who want to warn their other selves, those who want to start over, and don't forget a whole host of villains who figure they can take their chances in a new place.
(As a side note, Ray's striking "all natural look" – no makeup – also becomes a hit in Dark's dimension, with trendy types and the disaffected "going bare" in defiance of traditional values and mores.)
Things come to a head when Darkfire attempts to sabotage portal work, more of a lashing-out than anything serious, and he's brought emphatically to heel by the authorities. Despite the new interest in other dimensions, many people also see them as a threat: these other insane dimensions could come here and destroy or enslave everyone. Pro- and anti-portal groups clash, at first electronically and then in person. Ray is taken into protective custody, as the only real link with other dimensions and thus the only one with sufficient knowledge. He tries to fight his way out, but he's only one blaster. He's still treated well, despite this, and given whatever he wants, except the freedom to leave.
Four and a half years after Ray originally gets dropped into Darkfire's dimension, the Home Guard is well established, the first portals are working, and the Centrist party has just come to power in the world government. Determined to avoid the mistakes of Ray's world, Centrist and Home Guard scientists have deduced the location of the Rikti homeworld and are preparing for a massive invasion, to pre-emptively remove the Rikti threat. Ray's own dimension has not yet been found, as far as anyone can tell (or is willing to admit), but the confirmed existence of the Rikti proves that the technology is sound and that Ray's not a complete crackpot. Darkfire has faded into a footnote of history, rarely leaving his family's compound in Philadelphia. Ray has just been promoted to Special Services in the Home Guard and is expected to lead the defenses in the anticipated upcoming war.