A tiny bit of nit-picking: Rowan and Martin did continue to work together for awhile after LAUGH-IN; I remember them being the hosts of a couple of HBO specials in the mid-1970s. However, as you correctly note, Rowan's health was an impediment to working full time. Fortunately, he had invested his LAUGH-IN money well, so he did not actually have to work. He had also invested his partner's money well, so Dick Martin did not have to work, either. However, he found early retirement a bore; his pal Bob Newhart noticed this, and got him a job directing an episode of his sitcom, which led to the successful second career you mention.

Amusingly, Rowan is an off-screen character in the movie SUGARTIME, about the affair between gangster Sam Giancana and singer Phyllis McGuire. Apparently, he was an old boyfriend of McGuire, and Giancana was seriously jealous of him for awhile. That could have ended badly, but obviously did not (at least not for Rowan).