I don't like the way Johnponz insists it would never happen.
We saw something close this year, but the deep official signaled TD - so we had IW to fall back on.
Here in Germany (granted the quality of play is not what you would hope, but they also play NCAA with little kids who don't know the rules in Texas) it has happened, some of the officials in my association were working the game.
The runner gets caught from behind and the ball is knocked out at about the 15 - forwards into the endzone. ALL the players assumed it was a TB (or something, maybe they were just too tired after the long run), and NOBODY went towards the ball.
After a few seconds, there is really no choice but to blow it dead.
Please don't say it will never happen.