I saw no racism - we are all brothers "this was a question about a dollar collapse, not a devaluation." Actually it was 4 questions as a subset of "the" question. As far as I'm concerned "devaluation" to an extent that it would essentially be a collapse is included in the question and I like his response, except nobody will take on the specifics. Is that because nobody knows?
I believe no one is answering you because you phrased the Q as the dollar becoming worthless. No way the rest of World will let that happen as it would put everyone in the poor house. Its a purely hypothetical. In such a situation you would see massive global mayhem, closed borders, regional wars. It would be like a sci fi flick. Any tangible asset would be horded as we would be in a situation of barter. Gold is largely an inflation hedge, and a flight to quality hedge. In the situation you mentioned, sure gold would be hoarded, but so would everything else. You always have to be careful with gold; however, because in the situation of declining global consumption to the extent that it became deflationary (as we may now witness unless the US prints enough cash), gold would sell off, as long as the deflationary spiral was orderly.
It would seem a "coordinated" default of G7 sovereign debt would be more likely than an outright collapse in USD. If the dollar does well and truly collapse, global trade comes to a screeching halt, and you're talking about a couple of billion people literally starving to death. In that case we are so far beyond "predictable" outcomes it's really not worth worrying about.
Again, I've read the theory that the Chinese will jump all over this, let the dollar devaluate somewhat - not totally as you said - in order to become the biggest economy on planet earth. Some say they can literally make themselves #1 almost overnight and that they would be foolish not to do it. Btw, you may have read that China can maybe save the world's butt, but here is a nice re-butt-al: http://worldblog.msnbc.msn.com/archive/2008/10/09/1522548.aspx
World reserve currencies have changed before, and when they have, the results have been disasterous for the nation whose currency is no longer wanted. Its no longer an if, but a when, IMO.