Any Shows that were brought back after being cancelled or on a relatively long hiatus

Cafe Society
21

Always possible, but Jennifer Saunders stated at the end of the 3rd series in 94 that the show was done and she didn’t intend to continue it. Then changed her mind and did the 4th series in 01.

22

although, the OP did say cancelled or on long hiatus and I was going more with the hiatus part rather than cancellation.

23

If you count revivals of game shows, possibly with different MCs, then you have What’s My Line?, To Tell The Truth, I’ve Got a Secret, Match Game, Hollywood Squares, Press Your Luck (revived as Whammy!) and I’m sure a lot more.

24

Plenty of game and quiz shows fit the terms of the OP. A few examples:

Jeopardy! – hosted by Art Fleming 1964-75, revived as “The All New Jeopardy!” with Fleming from '78 to '79, retooled and hosted by Alex Trebek since 1984

Password – hosted by Allen Ludden (1961-75); brought back as “Password Plus” in '79 and hosted by Ludden until '80, then by Tom Kennedy until '82; resurrected as “Super Password” and hosted by Bert Convy ('84-'89)

The Price Is Right – hosted by Bill Cullen (1956-65); brought back as “The New Price Is Right” in a CBS version hosted by Bob Barker since 1972, as well as in a syndicated version hosted by Dennis James ('72-'77), Barker ('77-'80), Tom Kennedy ('85-'86), and Doug Davidson ('94-'95)

To Tell the Truth – hosted by Bud Collyer (1956-68), by Garry Moore (1969-78), by Robin Ward ('80-'81). Brought back for a 1990-91 incarnation hosted, in turn, by Gordon Eliiott, Lynn Swann, and Alex Trebek. Hosted by John Hurley (2000-02) in what is (to date) its swan song.

25

Beauty and the Beast was brought back after a fan letter campaign. Then Linda Hamilton’s character was killed off and the show tanked. I don’t recall how long it was off the air though.

26

We need to define terms here. If we’re talking about shows that went away then came back with the same cast, same setting, same writers, same everything, then the list is short – Taxi, Cagney and Lacey, Designing Women and a handful of others.

If we’re talking about shows where someone tries to revive the corpse with a new cast, new concept, etc. - like Sanford and Son/Sanford or The Odd Couple/The New Odd Couple then the list gets a lot longer.