When Jack Barry died. Joker had been on seven seasons, plus three years on CBS. I'm not sure if anyone could have kept it going longer than the two years it lasted. As for Barry himself, I always considered him to be a competent, but not spectacular emcee. I would not put him in the same class with Cullen, Kennedy, Barker or Martindale. IMO, he often looked uptight on camera.
Wiki seems to agree with the story about Barry planning to retire, FWIW.