What we don't know (not sure if this information is available or not) is how much of the £2.3 million they get each year goes into running their Royal duties. He or they can't expect to keep it if they're not doing them. They live in a 'cottage' which is actually a substantial house rent-free, through public opinion that would have to change.
I'm not sure they've really worked out the long term financial implications, Meghan could go back to acting, Harry could be paid to run his charities, but unless she consistently picks up hugely well paid roles its not what they currently get. I think an element of cake, wanting and eating may have influenced tbeir thinking.