No it would not likely have been the case. The Republic was still a ways from falling. And if the Jedi have intervened later, it would definitely not have fallen if they had defeated the Mandalorians. If they had intervened earlier it would have been worse. There was a reason The Emperor manipulated the Mandalorians into attacking first. And there wouldn't have been any of the deaths that followed in Jedi Civil War or the Sith Civil War, so the Republic would have been stronger if Revan had listened to the Council. If the Republic didn't fall from those two conflicts that directly followed the Mandalorian Wars, then it wouldn't have fallen if the Mandalorian Wars had lasted longer.
We can only speculate, the fact is though. This didn't happen, Revan did go to war - so debating about this won't get us anywhere. However Revan could never have listened to the council, because in his opinion what they said amounts to doing nothing, they advised caution, that was it, no battle plans or strategies. If Revan didn't leave another Jedi would have, it was inevitable.
The Council wad not apathetic, they were overcautious. You're clearly underestimating Revan's drive to get his own way. He was manipulative enough to be willing to let his own allies (sometimes entire worlds) perish if it benefited him in the long run. He would have found a way to use the Mass Shadow Generator. And even if there had been surviving Council Members that told him no. He could have simply defied them, like he did to go to war in the first place. With so many more Jedi embroiled in the Mandalorian Wars he could well have ended up with more Jedi turning.
I believe it amounts to the same thing. In the end they did nothing, that you can't argue with, its whether they would have thats up to debate, but they never did so I'm doubtful on their wisdom.
I concede that Revan had the resolve to get what he wanted, but he wasn't evil, or insane. He didn't truly want
to activate the mass shadow generator, he was a Jedi after all. It was a last resort, and last resorts would not have been necessary in a winning war, which is what it would have been if the Jedi intervened.
Blaming the Council for Revan's actions makes no sense and absurdly absolves Revan of any personal responsibility for the horrors he caused. Revan was effectively a traitor to the Jedi Order. It's not the fault of the people he betrayed that he did what he did. Revan made the choices, he alone bears responsibility for being "a dangerous force that waged war across the galaxy". Just because they didn't stop him and his followers by force doesn't mean they are responsible for everything he did.
The problem with your argument here is the council disagrees with you, they accepted responsibility for Revan's actions and admitted they were to blame. (Zez-Kai Ell also adimitted they were to blame for the fall of Ulic and Exar Kun.) Your also mirroring the arguments of Atris. Who also believed that Revan was a traitor, and that the council was not to blame for his teachings. Yet they disagreed
with her, as they would disagree with you. They admitted that they were arrogant in their teachings and had become misguided, they made a mistake. Joining the war may not have been the solution, but doing nothing certainly was not.
Obi-Wan blamed himself for the fall of Anakin Skywalker but it still was, at the end of the day, Anakan's fault.
It was not Obi-Wan's fault entirely. But arguably the Jedi were to blame. After all they taught him everything he knew, and let him be trained at such a old age. However this is a different situation, were Anakin was more involved in his own fall e.g. his revenge against his mother, and his relationship with Padme. Sidious also played a big part in coaxing him to the dark side.
But with Revan, the inaction of the council forced him out of the Order. Unguided by the Jedi and enraged by the Mandalorians, his fall was inevitable - only the Jedi Council
could have prevented it. Whereas in the case of Anakin they would have to remove Sidious, Padme and Shimi from the equation, which was impossible. Removing the Mandalorians from the equation was not.