Well yes. But it is the same as like quitting smoking and drinking as a heavy abuser from one to the other day. Your next few weeks will be not so cool. On this case it will be not so cool decades
Looking here the fertility rate is declining since the 1960s, so I wouldn't say 60 years is like quitting from one day to another, they had more than enough time to tackle the problem.
Oh yes yes. Of course the time would be enough to apply policies to tackle the problems created by this. However my experience of humanity so far is that those time will not be properly used to tackle the problems 🙃 therefore it will still feel like a cold turkey (IMHO)