First of all, your surgeon has a duty to answer all these quite
legitimate questions.  In fact, one could take the position that it is
necessary to fulfill the requirements of informed consent.
    I will take a crack at this however.  Since you've said there is a
concern of numbness, I'm thinking this is in the lower premolar area.
Some cysts are associated with dead nerves, but not always.  Cysts are
also common around impacted teeth, and if you have impacted teeth in
this area (canine teeth are probably the most common), they are even
more common.  They are usually associated with the crown of the tooth
and are called dentigerous cysts.  There may also be radicular cysts
associated with the root of a tooth.
    It is true that tumors sometimes arise in these cysts.  Most commonly
they are fairly benign, but care must be exercised in removing all
remnants of these tumors as there is sometimes a tendency to recur.  For
this reason it is somtimes necessary to remove all possible affected
bone, which may increase the chances of postoperative numbness.
    Oral surgeons of course are aware of the nerves in the area, and take
all precautions to keep the chances of permanent nerve damage to a
minimum.  Even if there is some damage to the nerve, it usually recovers
at least partially, but may take some time.
    Please get more information specific to your case from your surgeon.

Good luck,
Steve