at the end of halo 3, if you beat legendary, you know that master chief doesn't die. so they might come out with a halo 4, or they might start a completely new trilogy. regardless its going to be some time before they do.
first, it's not going to be called Halo 4, Bungie is no longer with Microsoft, who owns half the rights to Halo so that would include the name 'Halo' itself, second, since Bungies alone, I'm hoping it's story won't bomb like Halo 3's, anyone here could've made a better story than THAT! and I hope the stop mass producing everything. that's getting annoying. lol :P