They are done, 100%, this is the turning point and it's all downhill from here.
They depend fundamentally on volunteer labor and every decision they've made since announcing the API change has alienated that labor. The morale of every mod I know is in the tank.
The solution for this was incredibly simple. Reddit you want to charge for the API? Go right ahead, we all want you to make money.
But when the volunteer labor you need in order to function started complaining because this is going to kill the modding tools they need - you should have immediately, like next day, apologized for the oversight and promised free API credits to them until you sort this out.
This whole conflict could have been nipped in the bud, people would have grumbled a bit, but as long as Reddit got their act together in terms of tooling eventually, life would have gone on, and Reddit would have had their payday too (I doubt milking mods for spare change is the master plan here).
Instead Reddit decided to escalate. Declare war on the people who make their service possible. It was the dumbest possible move they could make for their business. The decision makers behind this must operate in one hell of an echo chamber.
This is the end, it's all downhill from here, I doubt they can recover.
Needless to say I'll avoid their IPO like the plague and so will many others.
10 years from now something else will have come along and replaced them and we'll all look back at this moment.