My guess is that both Christian and Mark Henry will be used as enhancement talent. Christian might win the United States Championship and some point, but Henry won't win another title. Both men had a great year in 2011. Injuries have caught up with both men this year, so other wrestlers have had to fill in the void. That said, guys like Cesario and Rhodes and Sandow could really use the rub from the two former World Champions.
Big Show seems to be getting the same title run as Henry did last year and I'm okay with that. I enjoyed it as I'm sure most of you all did. It was done right and Big Show just needs to knock people out. Not so much put them in a Hall of Pain like Henry did, but something similar and just win in dominating fasion.
Christian has added a few moves to his arsenal when he came back in 2012 for that short Intercontinental run. He can still put on good matches and I'm sure he can help a lot on SmackDown with the young talent.
I wouldn't call them saviors, but these two returning would REALLY help out the blue brand.