Unfortunately, on both your points that’s club ethos. Nobody said it wouldn’t be tough - replacing an international defender like for like isn’t happening, doesn’t mean irreplaceable - granted, evidence not great this year, that’s where we trust they get outlook & recruitment correct.
Outside of Celtic, I’m not sure Gallagher will favour a move away that may impact on his Euro’s place.
Tin hat on maybe, both players haven’t performed in weeks either & contributed to poor displays without criticism.