Your gerbils have lived much longer than normal, the average lifespan is 3-4
years. Anytime people acquire pets they must realize that eventually they
will pass on. A friend of mine told me once that losing a pet is a fact of
life, sometimes they live to old age, sometimes they get sick and die, and
sometimes they die unexpectedly for no apparent reason, if when you go to
acquire a pet and you aren't prepared for this you shouldn't get one yet.
This doesn't mean you shouldn't feel a loss it just means you should be aware
it will happen.