They will be replaced by what? The expression “new heavens and a new earth ” means that there will be a new government and a new earthly society over which that government rules.
سَتَزُولُ فِي هَرْمَجِدُّونَ ٱلسَّمٰوَاتُ وَٱلْأَرْضُ ٱلْمَوْجُودَةُ ٱلْآنَ ،‏ أَيِ ٱلْحُكُومَاتُ ٱلْفَاسِدَةُ وَرَعَايَاهَا .‏