I think that if Alonso should retire, Webber and Vettel would both understand that anything goes and that whatever arrangement they had no longer applies - it's open season on the title.
Of course, but what happens if Alonso DNF's after Vettel allows Webber through? Surely Vettel would be the deserving winner of the race and thus the WDC Champion (by 1 more race victory than Mark), but it would be a matter of if Webber would want to comply and concede position back to Vettel in order to give him the deserving win and WDC
Might I add that waiting until the end to do the swap could be a bit risky because Mark will be vulnerable to Alonso possibly getting by him throughout the race or possibly when they try to do the Vettel/Webber swap itself. If Vettel allows Mark through early on he can then be used as a blocker for Alonso, in order to allow Webber to cruise to victory. But the question is, what happens if Fernando then has some type of DNF (or falls out of contention)...
According to Red Bull owner Dietrich Mateschitz they won't use such underhand tactics, because basically they are too good for that. All I can say is, what a scummy hypocrite he is if they end up implementing team orders on Sunday
http://planetf1.com/news/18227/6496854/-We-don-t-manipulate-things-like-Ferrari-
'We don't manipulate things like Ferrari'
Tuesday 9th November 2010
Red Bull owner Dietrich Mateschitz has remarkably revealed he would rather miss out on the Formula One Drivers' title than employ underhand tactics like Ferrari.
Mark Webber and Sebastian Vettel go into the season-ending showdown in Abu Dhabi on Sunday trailing Championship leader Fernando Alonso by eight and 15 points respectively.
Either driver could yet clinch the crown, but it has also thrown up the intriguing scenario of Vettel potentially aiding Webber should the young German be in a position to do so in order to deny Alonso.
Team principal Christian Horner has already made it clear no team orders will be imposed, and instead a decision regarding assistance rests solely on Vettel's shoulders.
Mateschitz is also determined to see his team remain loyal to their sporting philosophy, as they have steadfastly done so this season.
That is in contrast to Ferrari's manipulation of the team orders rule for which they were found guilty after Felipe Massa allowed through Alonso to claim victory in the German Grand Prix in July.
Mateschitz is adamant his team will not sink to such depths as he said: "Let the two drivers race and whatever will be will be. If Alonso wins we will have been unlucky."
Speaking in Austrian newspaper Kliene Zeitung, the energy drinks magnate added: "I predict a Hollywood ending, with the worst case scenario we don't become Champion.
"We'll do it next year. But our philosophy stays the same because this is sport and it must remain sport.
"We don't manipulate things like Ferrari do. The whole world condemned them after what they did in Hockenheim.
"But we have turned out to look like idiots because we have not acted in this way.
"But we have never even thought about it as long as both our drivers remain in the hunt for the Championship.
"So a second place under correct circumstances might be better than a win on grounds of orders and confirmations."
Hamilton would undoubtedly acquire a perma-grin (permanent grin) if he does miraculously manage to win the WDC though, especially over Alonso by just 1 point 
It supposedly achieves a speed of 260km/h (the worlds fastest roller coaster) on that first incline section 
