Well, let's consider the normal functions of the bone marrow!
The bone marrow is a site for generation and maturation of many types of cells, including pluripotent stem cells, but most notably all living blood constituents. This includes red blood cells, white blood cells, and platelets. So, now let's take away the bone marrow. Without bone marrow, we cannot generate red blood cells. This means we have no way to transport oxygen around the body, and our cells would starve and die. Without white blood cells, we have no immunity. Remember that white blood cells consist of leukocytes, many of which are phagocytes that eat pathogens, and lymphocytes that kill pathogens and produce antigens for those pathogens. Thus, no white blood cells means we cannot defend against foreign invaders! No bone marrow also means no platelets, which means we could not coagulate our blood and any little cut or scrape could cause us to bleed out (although I guess this wouldn't be an issue if we couldn't make blood anyways!). In short, without bone marrow we would have no means of oxygen transport and no immunity, and we would surely die.
