The WT has to be the most reactionary organization in existence. I used to think they would make these decisions in a well thought out and business like manner but the decisions over the last couple of decades beginning with the decision to quit charging for the literature shows very little forethought.
Honestly, in the first world native speaking congregations, growth is almost all from born-ins or at the very least, individuals that have some connection to JWs (family mostly). The only real growth they are experiencing in first world countries is via the foreign language groups. And surely that's going to be decimated given they now don't have real territories any longer.
So, I'm not sure its going to have a huge impact for the time being. The biggest impact I see is a diminishing of the "importance" of the ministry. Shifting from trying to start studies (unsuccessfully in most cases but that's actually not the point) to just distributing literature or preaching is going to have an impact psychologically lowering zeal. It's already lower across the organization from my observations than it was say 20 years ago.
They've hinted for years that at some point they will switch to a message of doom or whatever phrase they were using. That's exactly what they should do for now. At least get the troops fired up for a short period of time until you can come up with some other BS.
I believe the GB totally buys into their own BS and they are counting on Armageddon coming to bail them out. May as well double down on that theory with a message of doom. You could also have a message of doom for a few years and then come up with a whole Jonah story whereby Jehovah decides to call off Armageddon due to the repentance of the world because of the JW preaching. Then, switch to a more mainstream religion. LOL