My mother has high, myopia doctor told her that the only way to cure them is intaocular lens procedure but what are the risks if it fails?..blindness?

Good result likely: Any surgery carries risk, and entering a "normal" eye for the purpose of inserting a proper corrective lense has some risk, higher yet in high myopia. Many however, have had this done and the results are mostly favorable. Always worth getting a second opinion in these circumstances from another local ophthalmologist. Blindness is quite rare in these cases.