The actor isn't larger than the character. The story for a character in a movie in no way shape or form needs to relate to what's happening in the real world.
Next time I watch Harry Potter I'll see if they skipped a film with Dumbledore. Pretty sure they didn't though.
I don't get the whole thing that recasting the role is disrespectful, or that it's acting like Chadwick never existed. If you ever watched Spartacus, no one forgot Andy Whitfield when he died of cancer. They ended the credits of the series finale of him saying I am Spartacus.