I would say no. "Contribution" is defined as
a payment exacted for a special purpose. The keyword is payment. When you make a campaign contribution, you are helping (in a rather minute way) to help buy the success of the candidate you are contributing to. Thus, a campaign contribution is little short of a purchase...which would mean that campaigns are little short of small businesses. Thus, to force refunds would be nothing short of a violation of business rights to me.
Okay, I intentionally went a little far with that.
But the point is, there is nothing I could see that would warrant contributors to receive their money back. If that's something the candidate would be intrested in doing, perhaps for populism's sake, than that's his
business.