Players will be able to escape from death no matter what. Even in Halo 3, running away was a legit strategy that worked out very well for the players who knew how. I enjoy the ability to sprint, I hate being slow. :/
That is indeed the brute chieftain from Halo Wars. The only brutes that we would see in Halo 4 would either be in service to the Sangheili or perhaps covenant remnants. However, Frankie DID say there wouldn't be any covenant in Halo 4, so brutes probably won't make an appearance.
Depends on the playlist. If you are talking about Infection, then no, that's common. Most people playing infection get bulltrues and die at the same time. However, if it's Team Slayer, then yes, lag is to blame.