Wow, only 1 reply to this thread? Well, here's mine...
The 773ER will definitely replace some 747s where the route demands the distance, but not the capacity. I think a lot of the 747s (especially the –400 variant) will be converted to freighters or combis, where the airlines want either a large freight capacity or a mix of the two, like how KLM fly (or used to fly) to HKG
with a combi, so they can carry both a substantial number of passengers and a high volume of cargo.