The only way I can see RI mattering is if Monica grows a brain.
Gervase is too arrogant to realize that he can't beat Tyson, so he won't make a move.
Monica basically needs to use the RI person to blindside Tyson (but he would be stupid not to play the idol, so she missed her chance to make a move this tribal council). In that case she just needs to take out Gervase and then Tyson next and try her luck against Ciera and the returning player. Its her only way to even have a chance. The only reason she was right to not make a move yet is because she would still be on the outs. RI player comes back, Monica is gone if Tyson plays the idol. The majority isn't Hayden, Ciera and Monica. It is Hayden, Ciera, and RI player. Now, they are stuck in the final three with her. She needs to make a move to have an argument to make to the jury (who already isn't a huge Culpepper fan and probably won't be moved by "I won a lot of challenges"). She cannot beat Tyson. No one but Hayden beats Tyson. So yeah, regardless of who comes back, Monica needs to take out Gervase and carve her own path to the finals rather than count on Tyson's. It is the only way she will have any chance of making an argument to the jury.
Other than that, odds are as follows:
Tyson - If he gets to the finals, he most likely wins, there are a few ways he doesn't but if it is Tyson vs any combination of Monica, Gervase and Tina, he's got the game wrapped up.
Monica - Can only even have a shot if she does what I described above, but even then, it is a long shot for her to beat Ciera or the RI player.
Gervase - Probably can't win. His game has all of the advantages and drawbacks of Tyson's, yet the dude was a straight, unlikable dick. He cannot win. Only think he has going for him is the fact that he is pretty tight with Aras in real life (though that could work against him since he backstabbed Aras, but Aras seem the type to take the game personally).
Ciera - IF she gets to the finals against anyone but Hayden, she probably wins. The jury isn't riding high on Tyson, but they will give it to him over Gervase, Monica and Tina. I don't think they will give it to him over Ciera. She will have Hayden's vote, Katie's vote (and with that Tina's vote), her mother's vote (assuming she isn't sitting next to her), probably Aras and Vytas's vote (swayed by Katie and Tina) and MAYBE Caleb (if he Hayden can sway him). She has the big move on her resume (drew rocks). If she gets to the finals, it will be a result of either brilliant manipulation or a good challenge streak. If she gets there, I think she wins.
As for the R.I. players:
Laura - She'd have an argument. She has been a beast at Redemption Island. That at least gives her some grounds to make a claim that she is deserving of the title. I'm not sure it would win the game for her, but if she sold it right, she'd have a chance. Downside, she's been helping Tina during challenges (for the sake of keeping the player she can most easily beat on RI). Therefore she has pretty much sent every juror to the jury. That's gonna create some bitterness.
Tina - Can't win. Its that simple. Even assuming that her daughter, Aras, Vytas, and Laura M. vote for her, I don't think she can win that one other vote needed. She just has too much going against her. She hasn't played a great game. She was voted out. She already won the million dollars. She came in second at every RI challenge she was in (except the last, assuming she is back in the game). If she is in the finals, she can't win. In fact, I don't even think she'd get Aras, Vytas and maybe not even Laura M. She'll probably get one to two votes.
Hayden - If he gets back in and makes the finals, he wins. End of story. There's no one who can beat him. He has played a great social game and won the jury over with his performance at the past two tribal councils. It was clear the jury was rooting for him. Hell, even Tyson, his opposition, seems to respect him. If he gets back in, he will be up against some combination of Tyson, Gervase, Monica, and Ciera. He will get Caleb's vote, Aras's vote, Vytas's vote, Tina's vote, Katie's vote, probably the votes of whichever two remaining players do not make the final three, and if Ciera isn't next to him, Laura M's vote. Hayden wins in a land slide if he makes it, probably 8-1 or 9-0. That said, I don't think he'll get back in (its an endurance challenge, which generally favors small women...though he is currently well fed, having eaten the day before, something neither Laura or Tina can say). So he probably won't win.
However, I gotta say, Hayden really came alive late in this game. His Big Brother skills have translated well. Big Brother is far more of a social game than Survivor (you are stuck in close quarters, you can't take a walk and cool off, you can't vote the person who annoys you off three days later, hell due to the HOH system you might not be able to vote them off at all and may need to kiss their ass...alliances are always shifting). Hayden has shown the ability to play the game in an intense manner (like the last two tribal councils) and then just shut it off and go back to the nice, soft spoken guy. And more importantly, people don't seem to hold his big moves against him. He is one of the rare players who can make huge moves without pissing anyone off. That is a very valuable skill in Survivor. I hope we see him back at some point.
