Believe me, if they had determined there was no safe way to re-enter orbit, they would NOT have just re-entered and said "oh well let's roll the dice".
They would have gone to the space station and lived there until their return could be arranged.
Check your history, son. Apollo 13 was in 1970; Skylab wasn't launched until 1973. The Soviet Salyut 1 (the first space station) wasn't launched until 1971.