Dollar-Rupee: Catastrophic fall, but when?

I have written two posts on how the dollar is likely to face a catastrophic fall against the rupee. and more generally against other currencies. Currently the following factors are keeping the dollar strong :

1. Net outflows of FII's from Indian Stock Market. It seems to me that on an average the FII's are withdrawing approximately 3000 crore rupees on a weekly basis (very rough estimate). Certainly this is putting a downward pressure on the rupee.
2. Several countries have huge dollar reserves. China, over a trillion dollars, and the Arab countries which price petrol in US dollars. They thus have a vested interest in keeping the US dollar strong. (but for how long?)
   

It is not clear to me how long the above two factors are going to hold the dollar up against the rupee. There is a third, a more fundamental factor, which plays a role in forex rates and that is the economy. If US economy worsens a lot than the Indian economy (which is likely the case), then fundamentally, the dollar SHOULD go down. It is point number 2) mentioned above which can cause a sudden panic selling of dollar, and make the fall much more sharper, I think. However, after having written two posts on this, I have realised one thing. I (perhaps even experts) completely lack the ability to make any quantitative prediction like when? how fast? etc. The dollar-rupee rate does affect me directly. Does it affect yours? Then ask yourself the question, if tomorrow China decides to offload its trillion dollar reserves, what happens? This wont happen as of now though, because that will hurt China perhaps as badly as it will hurt the dollar. The following article on BBC : The death of the Dollar? is worth reading. Again, it is an article, like my previous posts, lacking any quantitative predictions. Following is an excerpt from the article

..He [Prof Ngaire Woods] wonders whether the combined cost of foreign wars and domestic bail-outs is being seen as "a burden too far" for the US.

But for the dollar to lose reserve currency status would end what has been in many ways a huge bonus for the US.

It is sometimes described as the ability to write cheques that no-one ever cashes.