MLB rule on subs for injuries after you used the entire roster

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.

Why?

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.

MLB rule 7.03(b) (2021 edition):

A game shall be forfeited to the opposing team when a team is unable or refuses to place nine players on the field.

So if it's really the case that all but 8 players on your roster have already been used or are injured, your team loses the game by forfeit.