You may be correct, possibly the suit was never filed. I was Editor in Chief, not company counsel. Around the office, the matter was routinely referred to as the “Kirby lawsuit.” We certainly received a barrage of letters and demands from Kirby’s attorneys, many of which I saw.
If Jack and Roz had no interest in suing Marvel, you sure couldn’t tell that from Marvel’s POV. Their lawyers came at Marvel pretty aggressively.
I attended a panel at the San Diego Con, misleadingly titled, which turned out to be a Marvel-bash-fest MC’ed by Gary Groth. I don’t remember the year. ’79? ’80? Thereabouts. Groth opened with a diatribe against Marvel and its horrible unfairness to Jack. Then he turned the mic over to Jack.