is it a one time deal?

I hope not because snake is one of my main's.

I, for one, think that it is way too early to be thinking about another Smash game. But I don't think that Sakurai would get rid of the third party characters if there were to be another.

"The Brawl to end them all!"

^Yes. There's not going to be another one . This is the 'Brawl to end them all'. Now I'm just waiting until Mario stops having Parties so we can move on...

Assuming Smash Bros. continues for at least one more time around, they'll be in it. I believe Sakurai bought the rights for Sonic and Snake in the Smash Bros. series, not Brawl. If that's the case, there's no reason for this to be a one time special.

And just as a reminder, Sakurai hasn't totally dismissed the idea of at least one more Smash game. From the interviews Iwata had with him, it actually seems as though he entertains the idea of one more. I can't wait to see what his decision is.

I agree, I think we will see one more. He said there was things/modes he would have liked to have had in the game and wouldn't dismiss adding them into the next game.

Should be good

Of course there'll be another Super Smash Bros. This is a Nintendo franchise we're talking about, and a pretty lucrative one too.

Anyway, I imagine Snake and Sonic will be back in the next one. In fact, I suspect a few more third-party characters might show up.

Definitely wouldn't be a surprise. At least one.