It would be very hard for the USD to "collapse" because American demand drives the whole world economy. The US has a current-account deficit, Europe and East Asia enjoy surpluses, the net result is U.S. issues more and more dollars which are accumulated by the latter as savings/reserves.
A weaker USD vs. the Euro, Yen, and Yuan creates major political and economic problems in the surplus countries/regions a long, long time before it reaches "collapse" levels. As a result these countries/regions implement policies to weaken their currencies and restore the trade surplus, the water sloshes to the other side, and the cycle repeats.
For this reason, if inflation starts to rise it will probably be "exported" to surplus countries first - creating a tension between inflation-fighting and maintaining an adequately cheap currency, and bringing into question the practice of accumulating USD reserves at any price. When and whether this happens is entirely speculative, though.
Just for perspective, right now the USD is at the exactly same levels vs. the DM currencies as in the early 1990s, and even vs. the CNY (which was kept undervalued for decades) is still well off the 2014 lows. Hardly cause for alarm.
