You've got it right here, except for the order. They were already developing Pathfinder as a company by the time he went out there, then he played it and was glad that it looked like Pathfinder was the right call.
I was unaware of this. Though, I suspect that had he liked 4e a lot, Mon Motha would have eventually been scrapped as not needed. It's not a huge surprise that Jason was already working on updates. He is a guy who was very invested in the D&D rules. There's a reason that most of Living Greyhawk lived in feat of adventures written by Iuz(Jason)...they were likely to be extremely deadly and bend the rules fairly dramatically to be so deadly. He knew the rules very well and liked to abuse that knowledge to kill PCs.
I am reminded of Spring Revery Down Under in Australia. Guest of Honor was Jason. He was running a Special adventure written by him and they were keeping track of how many PCs he had killed compared to other DMs. I believe at the end of the weekend it was something like 22 PCs killed by Jason and 6 was the most for any other DM. Even with the same adventure.
That's a hard thing to say for sure. If we assume that most of the people playing Pathfinder now would have played 4e instead, you're probably right.
I think "most" is the key. If the people who switched to Pathfinder were split between 60% 4e and 40% other, it still would have meant that 4e would have had the staying power to go another couple of years. I think that 4e with all of these extra people would have SEEMED a lot more dominant to people. Perception is a big deal. When people consulted message boards to talk about D&D, instead of 4 people saying "4e is great!", 4 people saying "I think I'm just going to switch to Pathfinder instead" and 2 people saying "I hate 4e and Pathfinder, I'm going somewhere else", it would instead be 7 for 4e and 3 going somewhere else. New people coming in would have looked and said "Ok, so basically everyone is playing 4e. I'll buy those books." instead of "I don't know, I'm confused, there's a bunch of people at my store who play this game called Pathfinder, should I buy that instead of 4e?"
I think the perception that 4e had already lost...long before it actually had was part of its downfall. Which, for a lot of people, started with the announcement that Paizo had tried out the new edition and decided to make an entirely new game rather than write adventures for 4e. After all, if a company that ran Dungeon and Dragon Magazine for years hated the new edition so much that they felt they needed to make their own game...well, that surely meant the new game was bad.
Having run 4e at that same convention, I can tell you that the response was overwhelmingly positive. I had one player at one table who insisted on nitpicking the rules and complaining they didn't make any sense and I had one argument with a player at the end of the convention about the fact that square fireballs didn't make any sense and moving on angles being the same speed as straight meant that 4e broke the laws of physics. However, other than those 2 incidents, I ran probably 50 people through the Dungeon Delve or through the intro adventure and most people ended up really liking the game. People were lining up over and over again and standing in line for nearly an hour to play the Delve. I got roped into running it because they needed extra DMs.
It was only the truly diehard people who were opposed to it. Most of them were people who were mod authors for Living Greyhawk who were annoyed that they couldn't make things like Gelatinous Cube Monks and Animated Object Floors with 1 level of Warrior. Though, most of these people were good friends with Jason since he was a member of the Circle and dealt with them on a regular basis.
These people are fairly influential in the Organized Play/RPGA community however. I know most of them and a number of them ran conventions in their home cities with 300 attendees doing nothing but playing Living Greyhawk. When they came back from D&D Experience talking about how they hated 4e and their friend Jason had their back by keeping 3.5e going, it definitely affected things. How much? Who knows.