Xenorama is most probably right. After the first series for the rest of the Showa period, "Hayata" was most probably Ultraman's human disguise (ala Ultra Seven's "Dan Moroboshi:; Seven copied himself to look like the mountain climber Jirou Satsuma, whose life he saved when he first came to Earth, so Ultraman no doubt did the same by disguising as Hayata to resume his occasional work on Earth).
Some more info:
Back in 1969, Eiji Tsuburaya commissioned a story treatment called Ultraman Continues (Zoku Urutoraman). In it, the series' original cast was to be reunited, and Hayata would find a successor to the Beta Capsule. When Eiji Tsuburaya died in 1970, the story was completely retooled into Return of Ultraman (Tsuburaya; 1971).
The same story treatment was going to be used again in 1988, to coincide with the Ultra-Mania of that year, but production was halted by overseas deals, which resulted in the production of Ultraman: Towards the Future (Tsuburaya/South Australian Film Commission; 1990).
I'm guessing that Masaki Kyoumoto would have played Hayata's successor, being that he's a big fan of Ultraman, and was pretty active in the tokusatsu film/TV community, as well as being in high demand as a talented actor. (Masaki was the dubbing voice of Jack Shindo in the Japanese version.)
An article in Issue #68 of B-Club Magazine in 1991, where Masaki interviewed Susumu Kurobe (Hayata) and Sandaiyuu Dokumamushi (Arashi) had all three of them posing in Science Patrol uniforms and carrying Superguns (the Science Patrol's basic rayguns)! This may have hinted at the revival series that would've been.
As far as I know, THE Hayata himself appeared in the newer Ultraman movies.