[Crazy Jetty]

First off, all the butthurt on pure speculation is completely hilarious.
That aside, on a more serious note, Mattel is a toy company, and as a toy company would run it like hasbro.
It's not one or two guys that handle everything a toy company makes. Each franchise, GI Joe, Transformers, Marvel, Star Wars, all has a completely separate team of people running those franchise lisences.
Each team has a different way of doing things.
Mattel is no different. *IF*, and this is the biggest "if" ever, Mattel aquired the Marvel Lisence, they would set up a completely different team of people from the DCU team to run it.
And because of that, there's absolutely no way to predict with the 100% certainty that everyone is, that everything would go to absolute shit.
Mattel was all too willing to steal the Four Horsemen away, they may very will steal the MU people, too. They may not. There may be lisencing restrictions put in place by WB against Mattel having both (Just like Jason Abbadon said). It's a complicated matter that we don't know.

Secondly, just like there's no reason to believe everything will be ruined forever if Mattel got the lisnece, there's no reason to believe Disney will take it away from Hasbro in the first place.
Disney is all about money money money. They want that more than anything.And they'll sacrifice principals in order to get it. (They own a porn company for crissakes)
And leaving Marvel with Hasbro is not sacrificing anything to anyone. They have animation all over the place, even on the Hub. They played Warner Bros animations on Disney XD (And WB is a much bigger "rival" for them than Hasbro).
And Disney gets money no matter who makes the toys. Right now, Hasbro is successful with Marvel, and makes them money. if that doesn't change by 2017, I can't see them walking away from that.

Third, something no one's considered. I don't know exactly how copyright laws work over issues like this, but Hasbro may very well have some sort of copyright over the bodytype/style of articulation they use on Joe and MU, that protects them, and keeps Mattel from aping it. So even if they brought over every single MU dude, they may not legally be able to make something as sophisticated as MU was.

Fourth, 2017 is a *long* way away. Toy trends change really fast, and if a franchise doesn't keep up, the flounder (transformers), and die (DCUC, MotU). And a toyline can only handle continually releasing new variations of the exact same characters for so long before it starts bleeding (Star Wars). We may well be out of the 3.3/4" trend by then and onto something we can't even imagine at this time.

Fifth, and more importantly, THIS IS 2012! This is the year of the apocalypse! Who cares what happens in 2017?

Anyway, I love my DCUC, and have no love for Marvel Legends. So I would kill to have a DCUC styled Captain America, to stand next to my Superman.
And if Mattel did reinvent they're 3.3/4" lines and produced Marvel and DC figures that were on par with MU, then this would be a win/win senario for everyone. 6" Marvel figures as great as DCUC, and 3.3/4" DC figures as great as MU. That's my dream.