Lightning strikes can definitely cause the seperation of the bark from the sapwood. However, the time required for the bark to fall off is the variable for it could happen instantly or over a period of months to years.
With the leaders of this tree being so close together it is highly unlikely that the damage was caused by a lightning strike. For if lightning was the causal agent, signs and symptoms should have appeared in other parts of the tree by now. The callus tissue of the wound indicates that there has been a number of years between the injury and the present, therefore allowing sufficient time for the symptoms to surface. I say this because neighboring trees typically show the effects of an indirect lightning strike. This is sometimes due to root grafting or electrical current flowing through water found within the macropores of the soil. Either way the damage is evident.
Therefore, without seeing the tree or knowing its past, I would have to agree with Treetx by saying that the stress of the dramatic loss of foliage and energy reserves lead to its current state. Whether due to the large pruning wounds or the reduction in OEP (Oleorasin Exudation Pressure = responsible for xylem/phloem sap flow within the tree) therefore creating an entry point for alien entities. Regardless, damage is done and may remain a mystery!
