There is some confusion about what “Replay” does at the end of a game. Replay is just a challenge to the same opponent you just played. It is not a challenge on the same map. You still get to chose the map the game occurs on. As with a normal challenge, you can only chose maps you have access to. I verified this by using my normal (loaded) account and a brand new account with nothing on it.
Example:
Player1 has bought all the expansion packs.
Player 2 has not bought any of the expansion packs.
Player1 challenges Player2 on an expansion pack map.
Player2 gets to play on a map he hasn’t bought.
At the end of the game, Player2 can “Replay” (challenge) Player1 but will not have access to the expansion pack maps (even the one he just played on), only to the basic maps he normally has access to.
At the end of the game, Player1 can “Replay” (challenge) Player2 and will be able chose the expansion pack maps he has bought and normally has access to.