Chris, certainly any proposal about selling the property is actually not binding on the future business of the church. The church could gather in business meeting and vote to revoke that part of the agreement before you would actually sell. The will of the congregation can't be bound in the future like that unless you all sign a contract with the other church.
I'd echo Sandy's suggestion that you consider not resigning. Resignation would only remove part of your influence on the situation. Also if I were a pastoral candidate and found out that member of the search committee had recently resigned the board of Deacons in protest over an action of the church I'd frankly run the other direction. No one wants to interview with a church in active conflict.