The Equal Rights Amendment was a proposed amendment to the US Constitution with a 1979 deadline, which Congress later extended to 1982. The amendment failed due to being 3 states short of the required number of ratifications (not counting states that rescinding their ratification, something which the Constitution doesn't account for).
According to this question, if three more states ratified the amendment despite it being past the 1979/1982 deadline, the amendment would not become part of the Constitution. Nevertheless, Nevada ratified it in 2017 and Illinois did the same in 2018.
In the event that a third state ratified the amendment, what would be the next steps to determining whether or not the amendment can be legally considered part of the US Constitution? Would a court case get filed and go to the Supreme Court (and if so, who would file it)? Would something else happen?
What is the likely next step if three states ratify the Equal Rights Amendment after the deadline?