I'm sure it must have happened on numerous occasions. One I remember was Newcastle v Chelsea in FA Cup when Mourinho was in charge. The Special One made all three substitutions at half-time, and Wayne Bridge broke his leg early in the second half, so Chelsea played about 40 minutes with ten players. Incidentally, Carlo Cudicini was later sent off, so only nine players (with Glen Johnson playing in goal) finished the game.
not sure but a few years ago west brom were beating sheff utd in what was called the battle of brammall lane and the sheff utd players played on injuries and had the game abandoned as they went below 7men.
the score line stood though