Actually, wouldn't Ranma have been killed by Ebi-ten of the Seven Lucky
gods if Ryoga didn't exist? He was the one who stopped that wierd
fishing line thing just before Ranma's neck got slit.
Perhaps. It would turn out very different from the start, that's for
sure.
You have to remember - Ranma and Ryouga play off of each other like
superpowers in a nuclear arms race. Without Ryouga around, Ranma loses
most of his motivation to train. Thus, he's going to be a lot weaker by
the end of the series.
He wouldn't even know the Moukou Tahkabisha, since he got that as a
countermove from Ryouga.
I guess it depends on whether or not you believe the "one little
change transforms all of history" or "history corrects itself from that
change and can not be stopped" type of reasoning.
I've seen good arguements for both sides.