Donations to a non profit organization would be tax deductable and donators should be given a receipt.
No. He has no right to take the equipment. Companies provide sponsorships in order to develope goodwill for their business and to get their name out. I would do business with him. That would be a deduction in the goodwill column.
A "Certified letter" should be sent to the person stating the facts and requiring the return of the equipment. Is there a lawyer-parent in the organization. He can then ignore it or respond to it. The its up to the organization to decide how important it is the them to fight this battle.
i personally have fought many battles based on principle and other than the warm fuzzy feeling that it gave my to win I have gained little else.