HOW LONG DOES IT TAKE FOR THE BONES TO DETERIORATE AFTER DEATH?

It depends, what environment are the remains in? Is the
body buried or exposed to the elements? If the body was buried in a "sealing" casket and
if that casket was then placed into a "sealing" vault, the skeleton may remain for
several years. All soft tissue is fully decomposed in a couple of months. If however,
the body was buried in a non sealing casket and placed in a non sealing vault, then bone
decomposition will take place much sooner. All of this of course also depends upon if
the body was embalmed and if the embalming was done properly and
sufficiently.

Human remains that are left exposed to the
elements will decompose much faster due in part to microorganism activity that degrades
the structures. A common misconception is that the bones will remain intact
indefinitely, this is simply false information.