I don't remember who I mained in brawl, considering I played that game relatively briefly before going back to melee.
I think it was ike? I remember really liking ike when I first played him. I played marth a lot too.
in melee I primarily played samus, marth, sheik, and ganondorf, all of which I think would be in high demand to return. samus and marth are, unfortunately, not nearly as good as their melee incarnations, but I still believe marth would be missed sorely. you just can't cut the FE OG and expect to get away with it. Ike might be less missed, but he's a solid character and I really don't see any reason to get rid of him regardless of new FE games. he's one of the more popular lords in the series i think, and now that he's a two-time returning veteran, I think he'll be pretty safe in future smash games. robin and lucina will probably be replaced for newer FE characters.
ganondorf is obviously safe, being one of the iconic villains of nintendo, and samus is samus. none of the original 12 are going anywhere, let alone nintendo's flagship sci-fi mascot
edit: I played Wolf a ton too, and I'm pretty sure he'll be dlc within the year, along with maybe one or two newcomers.