If Roger beats Andy tomorrow and Simon beats Stepanek then there will be 3 players in the Group who have won two matches each. And as you know, only two can progress.
So how do they decide who gets the chop?
This is from the Master's Cup rule book:
If two or more players/teams are tied after the round robin matches, the ties will be broken as follows:
1. Winner of match between the two players tied;
2. Player with the highest percentage of sets won;
3. Player with the highest percentage of games won.