How likely is survival for a loved one with bone marrow cancer?

Depends:: Depends on a number of factors, like: the general condition, nutritional status, type of cancer, type of treatment given so far, any complicating factors. Some cancers, like prostate, are slow growing and survival can be for a long time. It also depends on the bone (s) affected by the cancer. Your oncologist should give you a prognosis, as he is aware of his situation.