The Bible does not say if demons will be imprisoned or allowed to run free.
There will be sin.
There will be marriage and children born.
Lifespans will return to pre-flood length.
Only the evil will die under 100 years old.
There still will be those who refuse to accept Jesus as Lord.
When Satan is released from the pit, he will again gather armies and attack Jerusalem.
God will say enough and destroy the earth.
But first there will be another thief in the night and the remaining Saints on the earth will be raptured.