the client does "own" those plans (unless your contract says otherwise) and they do not "expire" after a certain amount of time. He doesn't need to notify you or ask your permission to "use" them. When you contracted with the owner, your main deliverable is a set of plans that may be used for construction, now or in the future at the owners convenience. See attached ownership clause from a typical contract.
That being said, he must get the proper permits to do any construction or reconstruction. That means he must submit plans, sealed by an engineer that meet the requirements of the building department. Many building departments do not require upgrades to current code if you are only repairing damage. Some require it based on the cost of construction. Of course, that decision is made by the building department and might be on a case by case basis. If the plans examiner notices that the plans or your signature are dated 15 years ago, he may review those plans a little more closely and may require those revisions to comply with more stringent code.
Given that the client may want to make modifications to your plans, he can do that also, with or without your knowledge. But that would require the revised plans to be sealed again, either by you or by another engineer.
Your best bet to protect yourself is to include language in your contract or on the plans or both that releases you from liability if the client uses those plans in an inappropriate way. Such as changing them without involving an engineer or submitting them for permitting many years after they were prepared.