I highly doubt it.
Unlike Swagger, Miz has been a publicity machine for WWE. And even more then large, chiseled physiques, this is the type of superstar that Vince loves the most. While Miz isn't bringing in publicity in the traditional sense through ratings and PPV buys, as of yet, he is bringing a sense of recognition to the company based upon his appearances on Jimmy Fallon, Ghost Hunters, Are You Smarter Then a Fifth Grader, and the like.
Id look at him like an Edge. It took Edge a long time to break in to the main event scene, but since he's been there, he's never left. While i realize Edge paid his dues far longer then Miz did, Miz has still spent his time paying his dues. He's had to overcome far more obstacles in his 5 year career with WWE then most Superstars have, and he's gotten over each. I imagine that even if he's not seen as a Wrestlemania main eventer in the here and now(and he might be), they'll still be something big for him come Wrestlemania time. Following Wrestlemania, provided he's not in a title match there, he'll be in a high profile match, which he'll likely win. That should, like it did for Edge back in 2006, keep him right in the mix in the same way that it did for Edge.
Miz has also had a decent title reign, unlike Swagger. While Swagger's title reign was marred by poor feuds and terrible mic work, Miz has actually been involved in a decent feuds, and matches, with both Randy Orton and John Morrison. Other then his first title defense against Edge and Chris Jericho, Swagger's title reign was largely unmemorable. It wasn't completely his fault, but he didn't reallly do himself any favors either. Miz has done quite the opposite. Through each title defense, he's been opportunistic. Unlike Swagger, or even Sheamus, he hasn't been DQ'd in any of his title defenses. He's managed to defeat Orton(twice) and Morrison both within the bounds of the match rules that he's been in. And in doing so, he's been able to generate heat. The kind that makes people want to tune in to see him get his. He's been a great heel champion, unlike Swagger was. Despite him being booked as a vulnerable champion(there's a difference between "vulnerable and "weak"), he's managed to overcome being the underdog in every match he's been in. He's done so in underhanded ways, which again makes him a great vulnerable, heel champion.
The combination between the way hes been booked and the way he's generated publicity for the WWE almost ensures that Miz will remain in the main event picture, or at least the upper card after losing his title.
