I am wondering how long breast implants will last before needing more work on them?

Implant life. Implants that were placed before the 1990's had an approximate 10 year lifespan. We now have 7 years of surveillance of cohesive gel implants that show breakage rates of 3% and lower for silicone implants. So, frankly, there is no "expiration date" on the newer implants. They may last you lifelong.
Varies. Unless the patient is having a specific problem with her breast implants, there is generally no indication to remove/replace them. In other words, “if it ain't broke don't fix them”. Patients should disregard the myth that breast implant should be replaced every 10 years.
Breast implants. First science is not an exact, I have patients that have had them in for 20 years and then there are the patients that come back because they want to go bigger. My answer is 15-20 years maybe never gel is a better quality implant.
It Varies. Implants are not considered lifetime devices. Like all mechanical devices they are subject to failure. How soon this occurs can vary. Most implants can last well over a decade but they may fail earlier or much later. I have seen patients with implants well over 20 yrs old but I have also seen a few leak in just a few years. Most implants today come with a lifetime warranty.
How long? There is usually no need to change implants unless there are symptoms that need the surgical attention like rupture, or capsule formation. Lots of women had implants for a long time and don't need changing.
Varies.... That which causes the need for further surgery is not always implant failure. Reaction to silicone gel with hardening is more common. Newer generation cohesive gel implants do not rupture as soon as the older, but the gel they release can cause hardening. There are also aging changes in the breasts that can make the patient desire additional surgery. http://psinteractive.net/baug94.htm.