Real Madrid have their most important match of the year coming up and so they have no motivation to play for a win over Betis today. Betis, on the other hand, have an opportunity to get into the Champions League zone. Therefore, I think Real Madrid will lose today, they are already La Liga champions anyway.
Even if Real Madrid does not use their key players to play against betis, I don't think betis will defeat Real Madrid. Real Madrid performances are still alright without their best players. If betis tend to be tough in the game, it will end up with a draw . The game will likely be like the previous game Real Madrid played against cadiz, it was a game that ended with a draw but Real Madrid dominated and control the game more.