This is called force majeure or unavoidable accident.
It is a common clause in contracts that essentially frees both parties from liability or obligation when an extraordinary event or circumstance beyond the control of the parties, such as a war, strike, riot, crime, or an event described by the legal term act of God (hurricane, flood, earthquake, volcanic eruption, etc.), prevents one or both parties from fulfilling their obligations under the contract. In practice, most force majeure clauses do not excuse a party's non-performance entirely, but only suspend it for the duration of the force majeure.
Force majeure is generally intended to include occurrences beyond the reasonable control of a party, and therefore would not cover:
Any result of the negligence or malfeasance of a party, which has a materially adverse effect on the ability of such party to perform its obligations.
Any result of the usual and natural consequences of external forces.
Thus you try to convince him and also undertake to share some percentage of loss, if he insists on full compensation, you may ask him to proceed legally and you can challenge the same in court.