Your charitable income tax deduction for the purchase is not tied to whether you take the trip, but on how much you paid. For a charitable deduction, you are required to have paid more than the fair market value of the trip. For example, if the retail price for the trip was $4,000, and you paid $2,000, there's no deduction. If you paid $5,000, you can deduct $1,000.
If you can't make the trip, you can "regift" it by donating it to another qualified organization and deducting the amount you paid for it on your 2017 tax return.
