What's all the fuss about a prequel or sequel?
I think the work's fine as a stand alone.

The author was probably trying to do a character
sketch - more or less his/her (I don't know)
interpretation on how Ranma and Kuno would
react to a certain situation - namely the one that
the author made up.

The merit of the piece is in the interplay within
each character, but more, inbetween the two of
them.  It really doesn't matter who/how/why
Ranma was poisoned.  It is much more useful to
leave those weeks - where Ranma unsuccessfully
tries to adjust - up to imagination.  That's because
that's not what the piece is about.  It would distract
from the main portrait.

To write a sequel about Ranma and Kuno would
draw out that interplay too much.  As much as we'd
like to think so, we really get in the heads of these
characters, and in as serious a piece as this, it would
lessen the piece to attempt such a feat.  On the long
run, who knows?  Nobody, not even the author, could
create a situation which would be not be disputed.

I really think that writing a sequel or prequel, at
least in the way that people are demanding, would
take away from such a great piece of writing.

Just my humble thoughts,

-skeezy5, who foolishly attempts to guess at what was
    actually in the author's head...
    (Apologies to whoever you are... I don't even know
    your name...)