I don't understand why people worry ( for the US).
They are qualified.
They go on if they win the next game, they go on if they tie, and they likely go on if they lose by one. Actually, same goes for germany, but in their case even losing by 2 could be safe ( depending on the ghana-portugal final result)
But make no mistakes, There are no real alternative 'scenarios'.
The US will tie germany and both teams will qualify, with germany winning the group. Everyone is happy (well, except ghana and portugal).
Someone earlier posted the "scandalous" austria-germany game in 82. This is the same, only more obvious, because ANY tie works. They'll put in a fake effort for a few minutes, but the result is guaranteed.
WC 82, West germany - austria 1-0 both qualified, algeria eliminated
EC 04,Sweden- denmark 2-2, both qualified, italy eliminated
Wc 14 germany-usa 0-0 (or any tie), both qualified, ghana/portugal eliminated
They'll deny it, act all offended, but it will end up in a tie. Book it.

If i were a betting man, i would put a large sum on the tie.
Most obvious would be a 0-0, since it doesn't require any active fixing, just " saving energy", but it might look blatant. So maybe they'll go for an unspoken 1-1 ( with the us scoring first: if the us wins 1-0, they almost certainly both go, with the us first)
The only way for fifa to save face, is if portugal and ghana tie as well, or if portugal wins by 1. But if ghana is winning by more than 1, germany and the US will quickly switch to the "safe tie" mode
It sounds horrible, and in fact it is, but it is built-in in this format to possibly get to situations like this. Maybe if there is an outrage they'll change the format again, like after the algeria scandal (however nothing happened after the scandinavian fix).
Have groups of 3 where only the winner goes through, and the problem is fixed.