I posted this on the official SC2 forums and I thought I should let you guys know.
"My free trial expired a few days ago and I decided to check out the credits of the game.
Shortly after the credits ended I got a message saying I lost connection.
Guess what? It gave me the option to play offline.
I suppose if I would lose my connection any other way, it would work too. I haven't tested this though.
I'm pretty sure it's not intended for people with a 7-hour trial to play the whole campaign after the 7 hours have expired.
Well, I thought I would let you guys know.
Great game by the way, I love it.
Now I'll continue playing the whole campaign for free. But don't worry, I'm going to buy the game anyway really soon, because I want to play online too.
Good luck fixing fixing this bug!"
So, have fun playing the campaign for free while they haven't fixed it yet.