Unbreakable is limited by having available willpower. I see it playing out like so:
An Orc has 2 Willpower and Berserker 2. The Orc is broken, uses berserk to recover 2 strength and hurl itself back into the fray. The Orc is broken again while berserk. The Orc cannot use Berserk to get back into battle. Since the Orc was "broken while in a berserk rage, [he] cannot use this talent." The Orc spends the willpower using unbreakable. If broken again, the Orc will need willpower to get back into combat to use unbreakable once more. Granted, it doesn't say for how long " [you] cannot use this talent." I doubt it's 'forever' and would think it's for the combat, or until you've had an opportunity to heal/rest and recover.
You don't get it : once you are broken in a berserk rage, you are not berserk anymore. Or at least a power building player could say so, as it is the written limit of Berserker.
So the character now chooses to spend 1 WP to be Unbreakable.
Then he is broken again, but as he is not Berserk, as written he can use Berserk once again in the same fight.
Then he is broken again, but as he is Berserk, he spends 1 WP to be Unbreakable, and so on and on...
Of course Lucky is also part of the combo.
Hence my house rule limit : Berserk = once then you need to rest.
Considering the Berserk is not interrupted if you use Unbreakable is also an interesting way to avoid this.