Just thinking about what would happen if William decided to step down from the line of succession, and take his children out of it too.
Who would take over? Harry is next , but assume he wouldn’t want it for himself or his children. If he did, he would be a disaster and it would probably create huge ructions.
Anne when Charles dies would be too old. I don’t think her children are in the line of succession and there’s no way they would want it or be up to it. So then it would pass to Andrew, who would also be too old and not fit for it either. What on earth would happen? There would be no one fit for the task or wiling to take it on. The monarchy would collapse.