Major league rules. What happens if team used the entire roster and now a player gets hurt ???
When a player leaves the game he is done. There are high school rules that are subject to locality that allow a pitcher to reenter the game in a non-pitching role. However in MLB you get taken out, you are out - I think rule 303.
What happens when the manager is in the 17th inning and a player gets hurt and there is no one else? Well this basically can never happen in reality.
Because there are 4 other starting pitchers. So right fielder gets hurt, starting pitcher (that did not pitch this game) plays right field. If all of your other 4 starting pitchers enter the game and get taken out or if they are hurt... You play with 8 - bylaws will include an automatic out in the lineup.