Regarding the Romana thing, it seems clear in her second incarnation-at least in her debut season-that she's intended to be sort of a female Doctor (well at least the fourth one). In "Destiny" she briefly wears Tom's getup, and the pink outfit with white scarf she wears for the rest of that serial is pretty much the same idea.
I'm pretty sure she has her own sonic screwdriver as well.
I suppose they could bring her back with the time lords restored. The novels have her escape E-space but I'm not sure where the TV series should have the Doctor return there.