McNamara should carry on if he recognises the need to be bolder with both team selection and tactics. Not picking Hardaker and moving Tomkins to 7 was a missed chance IMO, as was not getting shot of Joel Tomkins after the first game and I would also have taken a punt on Joe Burgess after Charnley's showing in the first game.
He left himself with limited ability to make changes for the NZ game because the replacements would all have lacked match fitness, when if anything the Samoa game suggested a few changes were required for Australia.
Having said that, everyone talks as though if only he did X and Y England would have won. The reality is there weren't many gripes about the make-up of the squad, and had even Roby been available (let alone Sam Burgess) the narrow losses against Aus and NZ may well have reversed.
England just don't have quality from 1-17 available, even when everyone's fit. The backrow options available were poor, and the alternatives only marginally better (Westwood was a penalty waiting to happen in the World Cup, Ablett really isn't much better than what was available, Smith is a barely functioning halfback, who offers zero with the ball in hand etc etc).
Schoey's comments in the YEP are typical of the problem we have when assessing the coach - blames McNamara for lots of things, then rails about the problem being how poor SL is in comparison to the NRL. Given that any coach has to select well over half his squad from SL, it's frankly idiotic to hold him responsible for not beating Australia/NZ.
A lot of people were biased against McNamara when he took over. Personally I think overall he's done a good job - better than Tony Smith or Brian Noble IMO. Perhaps someone could take England further, but he at least deserves the series next year against NZ to show he can improve further.