Hello Kaam,
AdMob Mediation determines the network order server side and caches the order for 300 seconds so that it doesn't have to hit the server on every refresh. So the ads that are displayed from a particular network are streaky compared to AdWhirl, which randomly determines the order client-side on every refresh.
AdWhirl will continue to be maintained for now. When it's time to stop supporting AdWhirl, we plan to give sufficient notice time. Also, note that the code is open source, so it's possible that someone continues to maintain it.
Cheers,
Eric