Anything is possible and you can choose to do whatever you like, but bear in mind your choices have consequences. If you contract does not allow you to terminate the contract within a set number of days, time, what-have-you than you are obligate to follow through with the contract as it is stated. I suppose if you did not sign at closing then closing would not take place, but that opens the buyers to sue for damages if they choose to. You really should seek advice of legal counsel as others have stated before me.
Why do you want to terminate if you don't mind us asking?