I guess Im mistaken in the never although I do think it is very very rare for a show to survive an actor, especially the main actor, from getting replaced in the story and continuing. It really requires other popular characters to maintain the audience with one stepping in the new main character role and really good writing. But I really think we are discussing very different things.

My point isnt that changing any actor in a show spells its death but changing the Main character in an ongoing depiction of that character in a show or film does, hence why I chose the examples I chose.

This is the case with Robin was that the show ended one year after. Although it is a UK show and thus they dont really incentivize making 10 seasons like the US, I do wonder what the audience ratings were for the show in the first two series compared to the third.

What I mean is that West Batman can be seen as a different entry to Keaton Batman which is different from Bale Batman and so on. People have their own favorite Batmans, Spidermans, etc. but these actors are in their own reboots and not in the same narrative. This is the same for Sherlock and Bond. RDJ's Sherlock is very different from Cumberbatch and Ferrell or Brett and although they are portraying the same character, the interpretation and world is very different that they are independent, like a parallel world version of that character. I dont know enough about Jack Ryan to comment but it does seem to be similar to Bond in that although the character is the same, the stories arnt narratively connected and you are seeing Ford or Pine Ryan. Change John Krasinski in the ongoing tv show and not be a reboot and the change likely wont go over well. If in the Adam West tv show of Batman, West was suddenly changed with another actor and continued, it wont fare as well.

For Catwoman (and Dumbledore), the point is that the main character of the show isnt being replaced. Dumbledore was due to an unfortunate event and Dumbledore also isnt really in the forefront in the HP movies. Make a setting that Dumbledore is away from Hogwarts and while Harry Potter panics that D isnt there to help, the story can progress without him. There are many examples of this, that 70s show's main character's sister actor changing, Fresh Prince of Bel-Air mom actor changing, etc because they were a supporting character and not always at the forefront. Change Will Smith or Topher Grace (which they did) and the show likely wont last (and that 70s show didnt).

Im not saying that a character can never be recast or portrayed by another actor or the IP is doomed. Thats silly. I know age is a thing and that actors do eventually need to be replaced.

However, replacing or removing the main characters in a currently ongoing show that is supposed to follow the same setting and is not a reboot is very difficult to near impossible, regardless of the actor.

Witcher with Liam in a sense might go over better if they did do a soft reboot of the franchise. There will be another entry into the Witcher and other actors playing Geralt but trying to do so in an ongoing narrative most likely wont go over well.