If this hypothetical were to come to pass - I don't think the game would collapse, but the quality in many facets of the game would severely deteriorate as a result. I mean, sure no small measure of players use these tools, and indisputably, many of these players would have their experience diminished, but how many people would outright quit as a result is a greater question. People could ERP before this, and they could certainly still do it afterward.
Whilst I do think some of these tools are a woven part of the game or community, again, I don't think the loss of them would collapse the game, just deteriorate it quite significantly. It would be bad for them, for sure, and they wouldn't win - The reward of satiating those with a moral crusade going on wouldn't justify the price, but killing/collapsing would be a hard move. I'm willing to say I could be wrong though.
Gratitude is owed on both sides, I do think, but that depends on what you're giving gratitude for. I would argue some of the QoL features we have gotten have been as a result of third-party -- At least if reactions to the feature showcase they did is anything to go by. For what it's worth, I don't think community developments/creations outclassing or incorporating features that the game doesn't have natively is entirely a bad thing.
It's worth acknowledging that there are simply some tools that the developers would really struggle to replicate or have natively in the game, e.g., Teamcraft. Whilst it is a community creation, it's a very, very substantial creation to say the least with everything that it has now - They could expand their own trial synthesis, but by any stretch, it'd be difficult to compete with or replace. Something such as Lalachievements they probably could have natively. They already have a leaderboard for deep dungeons, so it is something they could feasibly expand on if they so wished.