This all boils down to politics and money - or lack of it.
Monza is bound to stay, there's political will to use some government money to keep it and it's probably all sorted apart from some detail.
Silverstone is a lot harder to call. It's the best supported race on calendar, hundreds of thousands attend year on year, but that in itself does not generate enough to pay the race fee - oh and zero political backing.
Difficult to see any fee discount lasting more than a year or 2, might not be enough to keep it next year.
My feeling is track may want it to drop off for a year, to show Liberty what its missing, and try to get better terms in future years. Could be mistake as this will definitely accelerate London docklands GP talks.
Spanish GP is doomed. Not enough backing either monetarily or politically.
German race I feel will go ahead, some compromises will be made to keep it because Brit GP will probably not happen. Mercedes can put money on table in Germany but can't bankroll British GP - isn't politics great.
Now Autodromo Rodriguez future race lies almost certainly in the hands of Carlos Slim, he brought the race to Mexico and it all depends if his love affair with F1 is over in face of the change in political climate.
My guess is he is waiting until the spotlight is on Mexico nearer to this year's race to show his hand. Could go either way as money itself is not the real issue. He may want to be seen as peoples champion, or blame political opponents for its loss.