There are so many things that were just theories in that we thought we could not attain, and now here we are,curing diseases, flying in the skies, now I hear there is a cure for cancer and AIDS. That which has been proven difficult to attain, humans have in times without numbers has beaten all odds.
So would not be surprise to hear that 100% human immortality is possible. By the curing of disease is kind of prolonging human  life which I can term as partial human immortality.
Although it will take decades to attain this, but once this is discovered, it will be very expensive for many.