He'd have had a great run, would have touched the world title scene and might have even won one, and faded into obscurity eventually. When you have a talent that is all gimmick no substance he doesn't tend to have staying power per se.
..He'd have become The Great Khali's dance partner, as a right-wing conservative Vince doesn't really want an EH RAB holding his belt for long if at all.
Then it would actually be the opposite of what you're saying. He'd build Hassan up to show what a despicable EVIL ARAB he is, and then have the super american super white-meat (Cena) babyface conquer him for the love of all that is 'MURICAN.
Why did he get fired?
The 7/7 bombings happened recently after he debuted so the Hassan character would have gotten WWE heat. Which is a shame, tbh - wrestling is fake until it's not, and then everyone's complaining.
If they would've gone a different direction (i.e. kept up the whole "not a terrorist, but you all have prejudices against me" gimmick), he would've been huge as a heel. Could've even done a face turn and it would've worked out.
Exactly, this is what his debuting gimmick was like, and if that's not a fundamental interrogation of the wrestling fanbase at the time then I don't know what is. Quite literally, his only initial "crimes" were whining, and acting as obnoxiously Arab as oh, I don't know, Sgt. Slaughter was obnoxiously American. And he was reviled for it. What an embarrassing time to be a wrestling fan tbh