The short answer is no, no-one who posts on prune knows what is going to happen, and I guess that includes most on the 3rd floor...
However, we are getting a couple of new A330's in the next couple of weeks, so my guess is that they'll be here for a while.
The party line is (and they NEVER lie) that the 343 will be staying for the foreseeable future, and the 346 will be going soon in order to save the costs of having a 'fleet' of 3 aircraft. Saying that, the intermediate plan is to keep the -600 going to JFK after the first ERs have arrived, and increase the service to 3 / day.
Longer term tho' get rid of the -600s, keep the rest.
I think that we should send the -600s to JNB all year round. But then again i'm about as low on the food chain as it is possible to be, so that won't happen!