If Tom Nook isn't in, then Blathers is probably the second most important. But if Tom isn't in I probably wouldn't expect another character.
Don't forget that there is more than one Tom Nook. If you travel to another town, there is another Tom Nook. While you never see two Tom Nooks in one place, it's still possible in Brawl.
The one thing this made me worried about is that if Tom isn't in the game, I can't see Nintendo getting together 45+ good character choices. Goroh and Nook were both acceptable, and now that they are supposedly not in, Nintendo is running out of valid characters. It is possible that the Assist Trophies are gonna knock out a few more of are other choices (Ridley, Olimar, Diddy) and if they are cut, this game will have around 40 solid at the most.
Don't screw up Sakurai.