Nearby lightning strikes are really a killer. Your case was worst-case: An open input. Best case is to have inputs shorted, but yours being open allowed the full potential of induced current to make the voltage across the input extremely high. As such, I would expect all solid state devices to be bad, and capacitors may also have arced internally.If this is a rare amplifier or has sentimental attachment, then you might have a shop go through it for you. But if not, you may find it's not cost-effective to repair. Might be less expensive to buy a new amp of the same kind.