Dire Bare
Legend
No, the Manual of the Planes states that if you travel "deep" into the Astral Sea, you'll eventually run into the astral dominions of other worlds, not the other worlds themselves. Although I'm sure you could travel to other worlds through via their associated astral dominions.Doesn't 4th edition explicitly state somewhere that other prime material planes (aka "World" or "Krynn", etc) are on the other side of the Astral Sea. Way out at sea as it were. But probably this side of the Far Realms.
In other words, if you planeshift from "the world" into the Astral Sea, get into your well-stocked astral dromond and travel far, far past Hestavar, you just might find the Fugue Plane someday. If you enter the Fugue Plane, and planeshift back to "the world", you'll actually find yourself in the Forgotten Realms.
Or you could just take passage on a spelljammer and travel the void (or phlogiston) between the stars to Toril!