Notice is for restitution of Conjugal Rights. As you want don’t want to get divorced, reply to him denying all the allegation made against you and also state that you are willing to live with him and promise him that you will join him.
The restitution notice sent with the intuition to compromise. if you refuse to restitute the conjugal right, he will make that as ground and may institute divorce suit. In such case you should appear before the court and plead your case.