Does a Chin Implant Ever Leak or Expire?

For many years chin implants have been made out of solid material (silicone, gortex, medpore) have nothing to leak and don't expire. After the initial healing period they  should remain, except in extreme circumstances, immobilized by surrounding scar tissue.

majority of chin implants are solid silicone and neither leak nor expire.  they can last your entire life.

Chin implants are made of a solid material, so generally there are no long term problems with them like breast implants had.
In the past, chin implants were shaped as a small solid disk that was placed in front of the jawbone. These implants were associated with erosion of the bone, so new "extended "implants were designed, which more evenly distributed the pressure on the bone and eliminated the erosion problem. If your implant was placed 15 years ago, it is likely you have the extended version. So, you're not likely to have any significant long-term problems.

The majority of chin implants placed are solid silicone implants. They do not leak or expire. There is an old-style chin implant that did have silicone fluid in the implant, but those have not been used for the last 20 years.

Dear Sharkitty,
To my knowledge, no implants used for cosmetic surgery "expire". There is a misconception that breast implants expire after 10 years. This misconception comes about because most of the warranty plans expire at 10 years (meaning if there is a leak, the manufacturer will no longer address it under warranty). If the breast feels soft and has not leaked, there is no reason to go in and exchange the implant.
Any implant placed in the body will be encapsulated with a surrounding layer of scar tissue. In the case of chin implants, this tissue is immaterial, as it is very unlikely to deform the hard silicone chin implant, and actually may help the implant feel more firm like the bone it is supposed to be emulating. In the case of breast implants, this surrounding layer of scar is more important. Ideally we want it to be soft and mobile, so that the only thing you feel is the mechanical properties of the implant (not the scar). If it is an aggressive scar capsule (meaning that it is thick, and starts to shrink the way all scars do), the capsule may start deforming the appearance of the breast implant, and can also become firm and palpable (we term this "capsular contracture").
Two implant-related reasons for revisionary surgery on breast implants are 1) implant deflation, or 2) capsular contracture. The wall material of either saline or silicone breast implants is a silicone elastomer (a version of silicone that has properties similar to rubber). It is very sturdy, but like any material that is constantly subject to deforming forces, it can fail (develop cracks, which lead to a leak). Saline implants (filled with salt water) will deflate if the wall fails, and the patient will know they have a deflation as the breast will shrink in volume. The old style silicone breast implants were filled with a liquid silicone, and if they developed a leak, typically the body would respond by converting the soft surrounding capsule into an aggressive one, and capsular contracture would occur. The newer silicone breast implants are filled with various levels of cohesive silicone gel (meaning it acts like jello rather than a liquid), so they will not leak out like the old silicone implants would. Because of this, they are probably less likely to form capsular contracture even after a leak, and this makes leak detection more difficult (since breasts augmented with silicone implants do not loose volume like saline implants do after a leak). [This is the reason that the FDA recommends surveillance MRIs after silicone breast augmentation.]
[As a side note, all of the newer breast implants (Saline or Silicone) have slightly thicker / more robust walls, so the leak rates are lower compared with older implants.]
In the case of solid silicone chin implants - they are not filled with saline, so they cannot deflate, and capsular contracture around the implant will make it feel more like bone. This is a long winded way of answering your question - I hope it puts your mind at ease.