Hairdressers don’t tend to really understand hair colour removers. Demi permanent isn’t much different to permanent. It should take most or all of the colour out. I can’t guarantee it will, but it doesn’t work for all permanent colours either. Staining can be an issue, but that can only be dealt with once the rest of the colour is removed.
Bacially, hair removers are non-damaging apart from be8ng a little drying. Just make sure to have a food deep conditioner handy and it will be worth trying. It’s always worth trying colour removers first.
Just remember, color FIX not color OOPS. Color oops is damaging.