50% for SC2 WoL according to the stats. However it is the multiplayer that boosts the IP and interest in the game. There is high chance that the IP would be dead or transformed into something else (WarCraft to World of WarCraft) if it was not for the multiplayer.
Also note that Blizzard went away from the idea that the campaign is a tutorial for the multiplayer. The units in the campaign are quite different. They use other means to train the player like challenge missions and special multiplayer games (with rocks blocking the ways so you could not be rushed, etc.).