Wild Bill is dead and I don't see how he would be coming back. He got shot in the back of the head while playing poker, which is consistent with the way he died in real life. If you want to semi-spoil the series for yourself, do some googling on historical bios on the characters.
If the series is about any one person, it's Seth Bullock, that was pretty clear from the beginning. I figured they would keep Wild Bill around for a few more episodes than they did, but they pretty much had to kill him in the first season to generate major conflict -- and get the series renewed!