I think it's probably the right thing to do, at least for the larger animals that should really be in a dedicated wildlife park/safari park with tons of space and a more dedicated focus on welfare, educating the public and conservation. I've never been especially comfortable with zoo animals and thrill rides in the same space.
However I do think such a move to a ride-only park will really show up Chessington's shortcomings as an attraction. I think for quite a lot of guests the zoo is the saving grace - take that away and all you are leaving people with is closed-down rides, unacceptably long queues for the ones that are open, reliability issues and below-average food and drink, and a crying child that can't be distracted from their disappointment by looking at all the nice animals. I wonder also how many autistic/ADHD kids use to zoo to decompress when the theme park all gets a bit much, so that's something else for the park to consider.
A lot of the TripAdvisor reviews also rate the animals and particularly the Animal Experiences a lot more favourably than the theme park, so I think they can expect a further drop in their review scores online.