Recasts are unfortunate but it’s something the movies had to deal with as well
It was such a shame to hear the news that Gracie Cochrane will not be returning to play Ginny for Season 2 but there must be a good reason for this and I respect her and her family's choice. She looked like great casting but I'm sure that whoever replaces her will do a great job. Of course Ginny is a major character in the story overall which is unfortunate but the silver lining with this situation is that her role is very minimal in the first book so at least they have a sort of clean slate for Season 2 when her role will be much more significant. I'd rather they recast now than between two of the later seasons.
To be totally honest, it was always in the realms of possibility that some characters would have to be recast in the show and it made me realize that this happened in the movies more than people might think. The first two are the most significant ones but I decided to include some student characters who have been cast in the show and may have larger roles than they did in the movies and also perhaps than the books.
Albus Dumbledore:
- Played by Richard Harris in PS and CoS
- Replaced by Michael Gambon for PoA, GoF, OotP, HBP and DH2
Lord Voldemort:
- Played by Richard Bremmer in PS
- Replaced by Ralph Fiennes for GoF, OotP and DH1 + 2
Lavender Brown:
- Played by two different uncredited actresses in the early films
- Replaced by Jessie Cave for HBP and DH1 + 2
Parvati Patil:
- Played by Sitara Shah in PoA
- Replaced by Shefali Chowdhury for GoF, OotP and HBP
Pansy Parkinson:
- Played by Genevieve Gaunt in PoA
- Replaced by Scarlett Byrne for HBP, DH1 + 2
Angelina Johnson:
- Played by Danielle Tabor in PS, CoS and PoA
- Replaced by Tiana Benjamin for GoF
Katie Bell:
- Played by Emily Dale in PS and CoS
- Replaced by Georgina Leonidas for HBP and DH1 + 2
Alicia Spinnet:
- Played by Leila Sutherland in PS
- Replaced by Rochelle Douglas for CoS
On another note, due to legal trouble the actor who played Vincent Crabbe in the films was fired but instead of recasting Crabbe they rewrote things so Blaise Zabini would take his role for the final film. The movies also removed Colin Creevey after CoS as the actor aged out of the role and elected not to recast him but to create the new character of Nigel who essentially took on Colin’s role from GoF onwards.
I'd love for the cast of the show to be as consistent as possible but I'll be realistic that this may happen again for a multitude of reasons. Hopefully if it does happen, it involves more minor characters. I know there are other characters that were technically recast in the movies but some of them are very minor characters in the books as well and sometimes these were hardly noticeable.