Not necessarily. A roof leak can be the result of damage done to only one area of the roof system or the result of a loose or missing flashing. A roof failure, however, such as improper roof system installation practices, incorrect material choice for the roof structure, or material failure, is generally irreversible.
Installing a new roof over an existing roof is acceptable but not generally recommended. Having a suitable surface to attached the new roof can only be guaranteed with a complete tear-off and inspection of the homes’ roof deck.
The best time to install a new roof is before the old one is leaking, and this requires a periodic inspection by a professional roofer. The other question is what time of year is best for installing a new roof. That answer is based on the weather.
The challenges of installing a new roof are numerous, including the danger of a workplace accident, along with the skill and knowledge associated with installing a roof system. Manufacturers generally will not issue a warranty if the product is not installed by a licensed professional.
Generally, the answer is yes. Unless the roof is at the end of its useful life or it was poorly installed, a repair can be performed. The real question will be, is it less expensive to repair it or cheaper over the long run to replace it.