^Title

Both Gen. Tullius and Ulfric dies?
Mede gets assassinated, but Penitus still manages to eliminate the Brotherhood?
Paarthurnaax lives despite the Blades' rebirth?

All those things are easily possible without the need for a dragonbreak, I would say.

-The winner of the civil war could fall off his horse.
-Penitus left notes for his successors to locate the Dark Brotherhood with.
-The Blades grudgingly go on without the Dragonborn.

It is highly unlikely another dragonbreak will happen.
Far more likely that things are simply never discussed again, except in the broadest of terms so that it remains ambiguous.

The Dark Brotherhood is never destroyed, either. Cicero and Babette survive your purge.

Recton the rectons.

Due to Dragon Break shenanigans (slaying Alduin):

Dovakiin assists both the Imperials and Stormcloaks

Both Dovahkiin's fight at the battle of Whiterun

One slays the other, eating the other's soul

Dovahkiin slays Alduin (that is to say, finishes the main quest)

Paarthurnax is killed. Blades are killed. Both by Dovahkiin at the request of the Blades and the Greybeards respectively.

Civil War is a stalemate.

Imperials keep control of the western half of Skyrim, it's name still remaining "Imperial Province of Skyrim."

Eastern Skyrim secedes from the Empire, becoming an independant country ruled by Ulfric.

Eastern Skyrim goes to war with the Argonians for the remains of Morrowind. Alternatively, Eastern Skyrim is taken over by the Aldmeri Dominion due to it's weakened state and lack of Imperial support (or rather, Eastern Skyrim is not an ally of the Dominion any longer, so the Thalmor take it over), which angers the new nations people, falling prey to what they were fighting against anyways (Elven rule in Skyrim).

Titus Mede II is executed either by the Player Character or an unknown Brotherhood assassin.

Dovahkiin (all possible Dragonborns due to Dragon Breaks) completes all faction questlines.

Dovahkiin (again, all of them), mantle Talos and become a part of him (possibly to counteract the slaying of Alduin, which is what the Thalmor want).

EDIT: I'm sleepy and studying. If I sound like my English is really bad and that my thoughts are disconnected, that's because they are. My thoughts that is.

Specifically, the Dovahkiin that does the Imperial CIvil War line becomes the King, the Dovahkiin that does the Stormcloak Civil War line becomes the Rebel, and the Dovahkiin that brokers the peace treaty in the MQ and ignores the CIvil War line becomes the Observer.

The time wound on snow throat might be big enough to sunder that tower, but I don't believe it's sufficient enough to cause a dragon break, nor do I believe taking Alduin out of the picture, no matter for how long or short would effect time in any meaningful way. Coupled with that, in my opinion there just aren't enough variables in the game to warrant a Dragon Break for gameplay reasons alone. I know you asked for what would happen if one did occur, but I can't see how one would.