It was a really weird area. If one faced the waterfall, from
the elbow in the river a few hundred feet ahead, one would see a
forest on the left and a vertical cliff on the right, at a perfect
angle from the waterfall.

You seem to be trying to give us an exact picture when your story
requires only a general, mood-setting, one.  And why is this area
"weird", exactly?  What kind of "perfect angle"?  A right one?  An
acute one?

wasn't long, but he would return in a week, this time with everyone
else.

How did Ranma get everyone else to come, especially camping?  We're
never told, and it would be _really_ hard to do.

But first, he had to catch his train so he wouldn't get to the
Tendo home too late.

Too late for what?  This train sentence is distracting, and doesn't
seem to have any purpose.

     "Do you think he'll do it, father?"
     "I truly believe so, my daughter. He has suffered for too
long. There is no other escape."
     "But it is so sad, leaving his friends and family behind."
     "Yes, it is, but above all one must consider his own
happiness. If he is not happy and cannot change his life, he must
end it."
     "I know... I hope he will be safe, wherever he is going."

Ah, mysterious voices.  I hope they have a point, such as being
Ranma's new girlfriend and her father.  If they're just here as
evidence that Ranma is faking the suicide, there are better ways.

     Kasumi frowned, ever-so-slightly. Those were the words of
somebody deep in depression, yet no matter how keen her senses she
could only feel an eery calm from Ranma. It could only mean... She
refused to accept it.

<clip>

affected, and now she had her answer. It had been buried deep and
now he was insane.

Not convincing.  If Kasumi is that perceptive, she should see through
the faked suicide.

He was still standing on the rock as he fell, and he looked up at
them, waving. "Good bye! I love you all!" he shouted before he

Rather an odd way to convince someone you're committing suicide.  He
actually sounds like he's leaving rather than dying.  Wouldn't it
be more effective if he faked severe depression?

Nabiki just stared at where the rocky point had been, the waterfall
below, unable and unwilling to believe that what she just saw had
the cliff, while Genma had walked away, wishing to be alone with
his silent tears. Cologne simply shook her head, ashamed.

I'm not convinced.  Neither Nabiki nor Cologne suspects anything?
Come now.  Genma's reaction seems off as well; I think he'd be in
denial, or ranting about his son being too cowardly to live.

     The last three, however, were far from being sad. They still

You really should give the names.  The fact that just about everyone
will guess isn't the point.  And why just three?  No Principal?
And where is Happosai?

     On a side note, Akane finally found out about Ryoga. She had
been crying near the foot of the waterfall and he had came to
comfort her. One small gust of wind had sent a little too much
water in the air for Ryoga's liking, but too late, Akane had seen
him. On that day, pigs could fly. Well, one of them did.

Was there a point to inserting this at this point?  You didn't make
much of anything out of the scene.  If you just wanted to start the
main story with Akane already knowing, you could have done that
without this insertion.

There are 
more than enough fics out there dealing with characters coping with 
Ranma's death. I am aware that Ranma killing himself in this 
fashion is 
OOC, but it's obvious he faked it, and the rest of this fic 
is about the 
others finding out about Ranma's new life and what they will 
do about it 
(not much idea there, BTW).

You're right that, on the face of it, this fic's been done before.
If your last line means that you have nothing new to say about
everyone's reaction to finding out about Ranma's new life, why
write the story at all?

Sometimes, the writing itself justifies a very well-worn plot.
This can be done by being unusually amusing, or by good, gripping
characterization, or sheer good writing.  This prologue doesn't
give the reader much reason to think that they're going to see
any of the above.  Unless you have a very unusual idea for the
rest of the fic, my advice would be to drop this story and
start another.  If you don't have an unusual idea, then my
advice is to put the story on hold until you get one.