I had one that broke (felled on it in a wipeout) on an offshore reef 1.5km offshore, after a 5 hour surfing session, so I was quite exhausted.

I tried to prone paddle to the shore, but it has been years since the last time I prone surfed, so I could not make more than 30 meters before stopping. What saved me was paddling without raising my torso and head from the board, and making 5 strokes with one arm, with the other resting fully relaxed laid on the board extended in front of me, and alternating. This way I could paddle the 1.5km in one go without problem, even feeling that I could have continued for a long time.