Los Angeles: Tax break for landlord for loss of revenue due to fire in a rental unit?

There is no 'tax break' for such a situation, other than that the missing rent revenues are not claimed as income, since they didn't exist. This situation is identical to having a vacant unit with no rental income, and is treated the same way for tax purposes. You still get to claim depreciation, insurance, taxes, and all other expenses accrued, and do NOT claim rental income, since you were not paid during that period.