Short answers, pulled from the story.
The Corwin Amendment is a proposed amendment to the United States Constitution that would have barred Congress from abolishing or interfering with slavery within any state. It passed Congress on the 2nd of March 1861 but was never ratified by enough states to take effect.
Senator William H. Seward and Representative Thomas Corwin, both Republicans and allies of President-elect Abraham Lincoln, introduced the Corwin Amendment. Thomas Corwin's substitute version, House Joint Resolution No. 80, is the text that ultimately passed Congress.
Abraham Lincoln addressed the Corwin Amendment in his first inaugural address on the 4th of March 1861, saying he had no objection to it being made express and irrevocable. He later sent a letter to every state's governor transmitting the proposed amendment, though the letter took no position for or against it.
Kentucky ratified the Corwin Amendment on the 4th of April 1861, followed by Ohio, Rhode Island, Maryland, and Illinois. Ohio, Maryland, and Illinois later rescinded their ratifications, in 1864, 2014, and 2022 respectively.
The Corwin Amendment failed because it was ratified by only a handful of Northern states and Kentucky, far short of the number required. It fell out of favor as the Civil War continued and never achieved its goal of preventing the war or preserving the Union.
Yes, in theory. No ratification deadline was ever attached to the Corwin Amendment, so a state legislature could still vote to adopt it.