From what I've read, dogs that go deaf as a result of the extreme piebald gene, normally loose their hearing within the first few weeks of life, it's not something that may happen 5 or 10 years down the road with a dog (at least where the parti gene is concerned).
"Deafness associated with piebald coloring is inherited in some breeds, but the presence of the gene by itself is not sufficient to cause deafness. For example, all Dalmatians have two copies of the extreme piebald gene (homozygous), but not all of them are deaf – there appear to be other genes involved as well.
However, it is important to eliminate other causes for deafness before coming to a conclusion that your animal is deaf due to the extreme piebald gene. Deafness in Samoyeds is not common (extreme white), but may be attributed to any of the following, or a combination thereof;
Congenital (present at birth) - Genetic (hereditary)
Congenital (present at birth) - Acquired (for example, dam exposed to toxic drug)
Otitis (inflammation) through bacteria or fungal infections in Inner or Outer Ear
Injury by accident or foreign body invasion
Old age (Presbycusis)
Drug Toxicity including General Anaesthesia
Noise Trauma
However, not all breeds with these genes (parti) have been reported to be affected. The deafness, which usually develops in the first few weeks after birth while the ear canal is still closed, usually results from the degeneration of part of the blood supply to the cochlea (the stria vascularis). The nerve cells of the cochlea subsequently die and permanent deafness results. The cause of the vascular degeneration is not known, but appears to be associated with the absence of pigment producing cells (melanocytes) in the blood vessels. All of the function of these cells are not known, but one role is to maintain high potassium concentrations in the fluid (endolymph) surrounding the hair cells of the cochlea; these pigment cells are critical for survival of the stria. Deafness in the Doberman, which is also accompanied by vestibular (balance) disturbance, results from a different mechanism, where hair cell death is not the result of degeneration of the stria but is instead the primary cause. Deafness may also occur later in life in dogs from other causes such as toxicities, infections, or injuries, or due to aging (presbycusis); these forms of deafness almost never have a genetic cause in animals and thus do not present a concern in breeding decisions."
Piebald or Extreme Piebald Gene – Deafness — Samoyed Club of America Education and Research Foundation (SCARF) Genetics of Deafness in Dogs