Mopub Network allocation inquiry



I have been using Mopub ad mediation for some months now for Millennial Media ad serving and I have
Marketplace turned on in my Mopub settings.

My questions are:
If I pause/stop serving ads from Millennial Media networks, will my ad traffic be cascaded down to Mopub’s marketplace?

Is it possible to give Mopub’s marketplace a higher priority than any ad-network I use for mediation?