Possibly what you want to get is a civil compromise where the person agrees not to assist in a criminal case.
Mr. Driessen is a former Deputy DA in Orange County with over 8 years of criminal law experience. Nothing stated on this site shall in anyway be construed as legal advice, or as creating any attorney client relationship. If you would like to hire Mr. Driessen, feel free to contact him at www.theocduiguy.com.
This is similar to your other question. You may wish to have a lawyer review your settlement agreement (a limited amount of legal work) to make sure your are not making legal "admissions", but as noted before, having turned down prosecution before, the DA is very, very unlikely to re-open.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
It could, but if they "victim" wants to press criminal charges even after the compromise, they can! Therefore, anything is still possible!