What if, because of an oversight or general orneriness, the 1787 Constitutional Convention did not provide for an amendment process?
There are actually multiple PODs here, but I think the discussion of all them can be contained in one thread. The multiple PODs involve how the lack of a Bill of Rights would have been handled:
a) No amendment provisions and no Bill of Rights or their equivalent in the articles, and the whole thing flops because the states don't agree. There would probably be another attempt, but this has massive butterflies.
b) The Constitution is forced through without a Bill or Rights or an amendment process amid general popular discontent. The question now is how long the new regime lasts.
c) Pretty much the Bill of Rights is incorporated in the original Articles, and it gets ratified, and an amendment process is omitted by an oversight. The issues that prompted IOTL the 11th and 12th Amendments are not fixed, so for a start the country is saddled with an unworkable process to elect the President.
Option c is interesting because, instead of the government collapsing or a new convention, there is the option of workarounds through creative interpretations by judges and officials of the language and in effect the growth of an unwritten constitution. This sort of happened IOTL with an amendment process, but one that is difficult compared to most countries.