I don't think the dollar is going to up and disappear, that would make no sense. Maybe doomed was too strong of word haha. Let me replace that with "In really dip ****". Right now, yes, the USA is A world's super power...but my opinion is that we are going to be outdone, if we are not already, by China or England.
England ? Really ?
England are like.. wayyyyyyyy less wealthy than the USA. The UK is also way way way less wealthy than the USA.
The UK is a great power, it forms part of the G8 (UK, USA, France, Germany, Japan, Canada, Italy and Russia) although russia is quite controversial, much of it's country is poor and has a very bad spread of wealth.
Within the next 20years the UK and Italy will likely be chucked off, and replaced by India and China.
China will almost certainly become a super power in the next 50years when it moves it's vast secondary sector to the wealthier tertiary and financial sector, Shanghai is what the whole of China will eventually be like.
But yeh.. the dollar is not doomed, the USA's prime position is however.
edit:
Yammy, Mak is correct. The USA is still the super power, there can only be one super power i beleive, the EU, UK and China etc are called Great powers to my beleif.