It is okay if a film franchise ends. Not every movie character or film series is James Bond. Some movie characters and franchises have their time but then just go away. And it is okay if a franchise ends. (Also not every film needs a sequel or to become a franchise but that is another article.)
Dirty Harry ended. Clint Eastwood stopped making the Dirty Harry movies and moved onto other things. There have been no efforts to revive the character with another actor (that I know of at least). The franchise had its time and ended. Eastwood made some really good films after the last Dirty Harry movie.
There has been news of another Terminator film coming out in 2019. Tim Miller, the director of Deadpool, is rumored to directing (that is not a bad thing). However the most memorable thing in the last three Terminator films might be Christian Bale's on-set freak out. I liked Terminator Gensis when I saw it in theaters but haven't felt the need to re-watch it since. It is hard to be very interested in another Terminator film.
I don't mean to pick on the Terminator series. The Pink Panther franchise should have ended with the death of Peter Sellers but producers tried to keep it going with a movie featuring clips of Sellers, and then tried movie with two replacements for Sellers before finally giving up (it seemed). Then years later Steve Martin tried to revive the series but it stalled out after 2 attempts. Neither film will be remembered as one of Martin's best and the first film might be among his worst.
I think maybe James Bond and Godzilla franchises can go on for years and years but even those franchises disappeared for a while. The Godzilla series has apparently ended a few times over the years but later came back.