1) Are there any 77W that DON'T have 3-4-3 configuration? It's not only UA. That is the standard on this model aircraft with most airlines.
2) Once were at it, is there any reason airlines are still purchasing 777's once they have the 787? Is there anything the 77W has over the dreamliner?
(1) There a few operators still using the nine abreast configuration including Singapore Airlines, JAL, ANA, and British Airways. Several other -200ER/-LR operators do as well, but the trend is towards 10-abreast to lower CASM and earn more revenue.
(2) The 777 and 787 serve different purposes in an airlines network. While some carriers have transitioned 777 flying to 787s, that's more to better optimize capacity. The 777-300ER offers more range than the largest 787-10 variant for one, and better cargo capabilities. They're two different aircraft for different missions and network needs. The current generation 777 line will remain active for several more years before transitioning to the 777X.