If they do that, it'll be a total betrayal of the thematic and character progressions made in SPECTRE.
It would be nice if they started Bond 25 without having to mention Madeleine, having just let the characters go off at the end of SPECTRE. In previous Bond movies, many, many final scenes included Bond with the Bond girl for them to never be mentioned again in the following film. I don't see anything wrong with this, although I suspect the production and creative teams won't leave it this way.
Sure. But that's perhaps more due to the fault said progressions were not nearly as developed and articulate as they should have been. For many casual viewers SPECTRE had exactly the back-to-business feel to it we often missed in Craig's tenure. The full impact of the final frames was largely lost on many.
I would prefer if Swann did re-appear in Bond 25. I'd love to see more of the relationship progress, but I wouldn't want the creative team to kill her off!! If she lives but never features in the franchise again, then I'll accept that the end of SPECTRE was just an audience pleaser. If she could return, and not die in the similar fashion of Craig's other women, then for me it would feel like more thought has gone into the script than merely using her as a pawn to kick-start the next movie.