Yeah, a few issues at play here.
1) Can Congress add requirements for ratification (such as a deadline) that go above and beyond the requirements listed in the Constitution? That seems dubious to me, but I trust our Supreme Court would be able to find a justification for it if they were so inclined.
2) Can a state cancel their ratification decision after the fact? This also seems dubious to me; it would lead to possibilities such as "2nd Amendment canceled after being in effect for 230 years because the legislatures of Massachusetts, Connecticut, Rhode Island, and Delaware decide they don't like it anymore."
3) Does the Archivist need to take action for an amendment to be considered ratified? Arguably no, as the Constitution makes no mention of such position at all. The Archivist could be seen as merely providing the executive branch's opinion on the current text of the Constitution. This opinion would presumably be challengeable in court if someone thought there was an amendment wrongly considered ratified (or wrongly considered non-ratified) and they were harmed by that decision.
Re 2: Agreed, there's a reason that a new amendment, the 21st, was ratified instead of states just reversing their decision on the 18th. (Of course, given the population distribution, an ERA repeal amendment could fairly easily be done now.)
However, a state reversing a ratification on an amendment that's met the requirements, and is now codified in the Constitution, is different from reversing one that's still waiting for more 'Ayes.' (1)
Regardless, I'm confident that our "originalist" judges in the Supreme Court would ignore some of the awkward Constitutional questions to thread a needle that specifically applies to this one amendment.
(1) Edit: Article 5 only mentions ratification. There's nothing in the Constitution about un-ratification. Further, there is precedent with the 14th where the reversal in 2 states was ignored/not allowed.