Guild Wars 2

So my friend doesn’t have the game at all, but the only option to buy the game from the site goes to the expansion. So my question is if he buys the expansion now, does he get a code for the base game right away?

If he buys the expansion it includes the core game for new customers/accounts. It will be one serial code but registering it will provide both. So your friend will not only have HoT when it is released but can begin playing the core game right away.