I Have Between 70 & 90% Bone Loss. I Was Told That Anything Over 50% Can't Be Saved, Resulting In The Removal Of All Teeth. Is This True?

If those percentages are accurate, that is severe bone loss and if that amount of loss is generalised (all areas) then yes, you wll probably lose a majority of your teeth. It will need to be assessed by a periodontist to see what preventative measures can be taken, if any. You see, once you lose bone height, it cannot be regenerated, only halted and then maintained. The number one reason for tooth loss in people over 30 is periodontal disease, so you must get on top of this, pronto.