He told NBC that if they gave him the early evening, Monday prime time slot he wanted for ST's third season, that he'd stay on as producer. NBC accepted that deal, then they switched ST back to an even later timeslot - on Fridays, when the young, core audience was out enjoying the end of their university week. Having threatened to walk, he carried out that threat. The show was not "dying" at the end of Season Two, although NBC wasn't happy with its ratings and wanted to try a better timeslot. The final episode of TOS for that year was a backdoor pilot for another TV series, "Assignment: Earth". No, he turned down involvement with TNG several times, IIRC, but Paramount was going to make a new series with GR's involvement or not. Paramount wanted his return to active involvement as part of the media hype.