Assuming you don’t have voting members of your organization, that the “committee” is your governing body, and that the festival is your principal activity, you have a lot of latitude in deciding what to do. While your board controls the money, it isn’t yours personally and you have a duty to use it for the purposes of the organization.

My immediate reaction is that it is probably a shame to discontinue the festival just because a majority of the present board members have lost interest.  You don’t say how long you have run it, how many people participate, or how it is received by the public. If you have a “substantial” amount in the bank, it doesn’t sound as though the event would fold solely for lack of financial support.  The issue is not whether some of you have lost interest, but whether the public has lost interest in what you do.  Will anyone miss you if you are gone?

You could give your substantial fund to a new organization to continue the work.  More easily, the majority of your committee could resign so that those who want to continue can add new members and pick up where you have left off.  That would seem to be the easiest transition if you are willing to let the festival continue with others leading the way.  Others who care might be very willing to join the effort.

If there really isn’t much public interest in the event, you could spend your last dollars on a fireworks show as the ultimate finale for the festival and then dissolve.  (I am assuming your substantial amount would fund a traditional community display and not a war of the worlds.)  Or you could forget the fireworks, go quietly into the night, and give your remaining funds to an organization that will continue to support your town in some other way.  In making your decision, I would urge you to ask what is best for the community.