Concept:This is a third conditional sentence, which describes an unreal past condition and its imaginary result.
Explanation:The clause "If the school had been destroyed" uses the past perfect tense.
This shows that the condition is purely hypothetical and happened in the past.
For such a condition, the result clause must use "would have" followed by the past participle.
The correct expression is "would have had to go", where "had to go" is the past form of necessity and "would have" connects it to the unreal condition.
Option A "would go" and Option D "would be going" refer to present or future time, not the past.
Option C "would have to go" is also present or future in meaning.
Only Option B correctly expresses the past unreal result.
Answer:If the school had been destroyed, we would have had to go home.
The correct option is B.