Dear Tennessee fans
Please stop watching this clip like it is the Zapruder film:
The fact is that Alabama blocked your field goal and gained possession.
Yes, Terrence Cody removed his helmet, but it doesn’t really matter whether it happened before or after the clock hit zero.
Alabama was going to get the ball.
Penalties about the removal of headgear are assessed on the next play, just like penalties for excessive celebration (which do not negate touchdowns.)
If you’d like, we can go back to Bryant-Denny and mark off the 15 yards, and let Alabama take a knee. But we can’t, because there was no time on the clock, so there is no mark-off and no ensuing possession.
You played one hell of a game, against a team you had two weeks to prepare against. You are clearly on the way back to competitiveness, which is great for the SEC.
But don’t cheapen yourselves with conspiracy theories and meritless complaints.

http://www.ncaapublications.com/Uploads/PDF/Football_Rules_5_2204c0005d-845f-4813-8391-54f15136079d.pdf
And let's go ahead and cover the scenarios that may come up in discussions based on (a) time left, (b) who had posession, and (c) any penalties:
Scenario 1:
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(a) 10 seconds left after play is dead
(b) Alabama recovered
(c) Cody was flagged
Outcome: Alabama would've been penalized 15 yards from the spot of the recovery and it would've Alabama's ball 1st and 10
Scenario 2:
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(a) 0 seconds left after play is dead
(b) Alabama recovered
(c) Cody was flagged
Outcome: Game over -- helmet removal is a live-ball foul treated as a dead ball foul and would've been enforced on the subsequent play, however, since there is no time left on the clock, there can be no subsequent play and the game ends.
Scenario 3:
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(a) 10 seconds left after play is dead
(b) Tennessee recovered
(c) Cody was flagged
Outcome: Tennessee ball and 3rd down, only they'd be 15 yards closer since there was a "next play" to enforce the helmet penalty on
Scenario 4:
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(a) 0 seconds left after play is dead
(b) Alabama recovered
(c) Cody was flagged
EXTRA (d) Game was tied when time expired
Outcome: Regular period expires, overtime starts and the personal foul against Alabama would be assessed on the subsequent possesion (either it'd move Alabama's starting point WAY back if they got the ball first, or move Tennessee's up if they got the ball first)
Scenario 5:
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(a) 10 seconds left after play is dead
(b) Tennessee recovered
(c) Cody was NOT flagged
Outcome: Tennessee ball and 3rd down at point of recovery.
Scenario 6:
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(a) 10 seconds left after play is dead
(b) Alabama recovered
(c) Cody was NOT flagged
Outcome: Alabama's ball and 1st down at point of recovery.
…and finally what actually happened:
Scenario 7:
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(a) 0 seconds left after play is dead
(b) Alabama recovered
(c) Cody was NOT flagged
Outcome: Game over;
…but oddly, here what REALLY happened:
Scenario 8:
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(a) 0 seconds left after play is dead
(b) NO ONE recovered
(c) Cody was NOT flagged
Outcome: Note item (b). If you watch the film of the play, the ball comes to a complete stop before the Alabama players scoop it up. Once a live ball comes to a complete stop in the field of play, the ball is dead. It can’t be picked up and advanced or “recovered”. Check out page FR-79 in the rulebook PDF at the top of this post. Scroll down to Article 3, item f. That’s REALLY what happened. So, if there was time left after the kick and no one had touched it, Tennessee would’ve gotten another shot on the subsequent 3rd down. They actually “recovered” by default.
Now, did Tennessee deserve to win that game? No. They had missed opportunity after missed opportunity. But they do deserve the fairness of the rule, which in this case (as in so many cases) was just overlooked.
The clock had hit 0.0, but the ball was recovered by Alabama.
Ergo, no re-kick.
The helmet rule is in reference to excessive celebration, which is why it is assessed as a dead ball foul. Otherwise, excessive celebration flags would nullify touchdowns instead of being enforced on the subsequent play.
Please read the relevant rules linked from Jamie's comment. They come from the NCAA, not the SEC or RammerJammer.com.