There will be ways to maintain order. Maybe neighborhoods band together to hire peace officers etc. This idea that civilization can't exist without central authority is simply wrong. Civilized people create governments, governments do not civilize people.
In the same way it's wrong to assume that every government has to be bad, just because our current ones are kinda bad.
Maybe there are ways to manage a society in a decentralised way, just like Bitcoin is a way to solve
some currency problems in a decentralized way.
I haven't heard many convincing ideas in that regard though and it isn't really helping that quite some liberatarians/anarchists use the word "free market" like it's some magic that will automatically cure all problems.