[Tuor in Gondolin]

As I'm rereading UT now, it's remarkable how much JRRT improved on Isildur in his later writings on him and the Gladdeen Fields, unlike PJ's cartoonish guy, in the movie getting lucky taking out Sauron and his almost Snidely Whiplash leering in deciding to keep the Ring and cheerfully abandon his men.

Projecting an alternate world where Isildur did throw in the Ring what happens? A more solid North Kingdom, with isildur and his older sons surviving. And what happens with the elves. Presumably the Three Rings lose their power at once. No propped up Lothlorien. And there's still the problem of the majority of Men in the east and South, corrupted by Sauron.