Satan, demons, devils and angels"

So will demons be destroyed by G-d after the revival of the dead as Christians claim or they will be given other functions?

Judaism does not believe that anything is inherently bad. Even those angels=messengers who are sent to challenge us (what you call demons...) are meant for our benefit. As soon as any messenger finishes his/her mission, they cease to exist. Accordingly, you now understand that there is nothing to destroy...