Jen Bowman, Broker Associate
Typically you can terminate the contract within the due diligence period with or without the seller's signature. Yet, as mentioned by my colleagues, it's best to get the signature of the seller on the release agreement to the earnest money.
Also, typically "your agent" isn't YOUR agent; so always keep in mind that unless you have a contract with "your agent" to be a exclusive buyer's agent, then they represent the seller and the best interests of the seller. All they owe to you is honesty, competence and things along those lines.
So, typically, you will need to make sure you get your intent to terminate communicated to the seller (in writing) within the due diligence period, with or without their signature. Typically you will have the right to terminate, if it's done within that time period.