I don't understand why they would need to delete the work of non-cooperating past contributors; they could just apply the contract to new or relicensed data, and the previous license to the old. Copying it would require satisfying both the license and the contract. Is the present material licensed in a way incompatible with the new regime? Indeed, is it, being a compilation of facts, subject to any conditions at all? (Isn't that what this is all about?) If not, why does it matter whether they agree to anything?
The scrupulous way to do this would be simply to fork the present project, compete with it under the new terms, and see who wins.