From what I understand it, Monty had the story setup written down and saved for up to season 7 I do believe already. I can't promise how much they went away from it though.
Montys death (once we talk about it past the fact that a really talented artist died just as his vision got started, and that's horrible) is actually an interesting line to draw in RWBY's history. Monty did some things very well: Tremendous and clever fight scenes, having a great idea on how to design characters (a large part of what sold me on the show was the character designs. Even if the animation wasn't amazing, all of the main cast is more or less perfect in terms of unique and awesome looks, especially Ruby, Weiss, and Yang), and basically knowing how to keep people invested: One of my favorite Monty things is that every major character in RWBY in the first couple seasons had a costume that had pockets clearly designed in it, for convenience for cosplayers. That's such a minor thing but really clever in marketing yourself to that fanbase.
That said, there are some things that were clear flaws as well. Monty wasn't a great story writer, and that led to many problems in the first couple seasons. RWBY kinda has struggled, imo, to figure out it's identity. In Season 1 & 2 it was mostly a teen drama with some awesome fight scenes. The problem is most of the teen drama stuff was centered around a character a lot of people didn't care about, and that fell flat. Also, it's a show that sold itself to people through it's trailers, which featured really really fun fight scenes. The Red, White, and Yellow trailer were mind blowing 5 years ago, and there were only 3 legitimate fight scenes in the entirety of season 1. Now all 3 were cool as shit, but that's over about 20 episodes. That's a lot of weekly episodes without the thing that sold the show, basically. Also, Monty was... flighty. He loved the rule of cool, and would push things just because "Well this is an awesome character design, so we are gonna use this character a bit" with no real plans for the character themselves. His love for side characters at points hurt some of the main characters progression.
But once Monty passed, things had to shift. Nobody else in the company can make fight scenes like Monty, and honestly, they haven't had a fight scene touch one of Montys true best since (Though Volume 5 Episode 4's fight scene, imo, comes close), so they had to focus to the story, and it's been mixed results so far. They basically changed from a teen drama to a full on straight anime style adventure, and... I'm still not sure that was the right call. I think the main plot could have used a couple more years to develop, but here we are. Season 3 was okay, Season 4 was not. Season 4 they tried to change how they animated things and basically took way too big of a bite to chew on, and many things felt rushed and poor. The good news is, Season 5 so far has felt like a significant step up from 4, at least in parts. Without going into spoilers for those who haven't watched it, I've really enjoyed the Yang and Weiss story arcs, have been "eh" on the Ruby one, and the Blake one has just been there to me for a while.
And rant over.