I wonder how a Fire Emblem Healer unit (Serra, Edean, Ethlin. Not picky. Actually I'm picky, I want Ethlin cause Fire Emblem 4 was crazy.) would work in Smash. Upgraded, obviously.
If there would be an FE character with a staff, most likely case it would be either Leif, Micaiah or Anna, since they have a secondary means of fighting(Micaiah with Light Tomes and Leif & Anna with swords).
That said, I can't exactly imagine a Healer being added to Smash since that is sort of Wii Fit Trainer's gimmick, with being able to heal herself. I'm not counting Robin since he heals through attacking. Wii Fit Trainer can heal herself without attacking. Despite that, there are staffs that can be used that don't rely on healing, like Rescue, Warp and Ward/Barrier.
How do you know My Unit is likely to return in a new FE game?
There are no guarantees, although so far since appearing in FE12, it's been used since then, even if it's only appeared twice. That said, if a remake of FE7 were inevitable, I'm pretty sure it would be used again.