I'm sure you can still make a p2p connection with your friends without going through battle.net and play for free if they require payment for battle.net. If nothing else, I'm sure it'll have a LAN multiplayer option and people will use a virtual LAN program.

Actually, you're right. If battle.net requires payment, Blizzard will lose a bunch of money because people will do multiplayer by virtual LAN and won't need a unique CD key.