I am sorry to hear your mum has multiple myeloma (MM) and is now on dialysis. More likely than not, hers will have been a sudden and unexpected illness, and will not have given either of you much time to adjust to the concepts of illness, marrow cancers, and dialysis.
Regarding survival … I am not a personal fan of putting duration boundaries to survival as we are all different, and have such different responses to pretty much any treatment, that survival time can be very difficult to predict in any one individual. As a result, we tend to fall back on reported series in the medical literature but - in the case of MM - many of these are now 2 or more decades old and there are yet to be a similar set of newer studies to look again at the survival data in the light of newer developments.
In the intervening time, many newer treatments: bortezomib, lenalidomide, thalidomide, a number of other monoclonal antibody drugs (or immune-modulating agents) … these all have a ‘-mib’ ending … and even marrow transplantation have all been added to the MM war-chest.
For those with renal failure from the outset, treatment with haemodialysis using so-called ‘high cut-off’ dialysers (artificial kidneys that are highly permeable to light chains and can significantly remove them from the circulation) has certainly helped some who were initially dialysis-dependent to shake free from dialysis. This latter option (the use of high cut-off membranes) was very enthusiastically embraced from around 2010 to 2013/4, and to be truthful, we were buoyed by some early successes here, too, but as the cost is high and the successes patchy, enthusiasm has waned somewhat from the headier early days 3-4 years ago.
Obviously, I do not know the details of your mum’s case - nor which (if any) of these drugs and options she has been treated with - and your treating team are in a much better position to advise you with certainty. But, I think it is fair to say there has been a significant improvement in survival in MM - even for some who remain dialysis-dependent - though I am afraid that renal failure and dialysis do still have a significant impact on survival.
I am not sure if that helps - clearly I can’t use any specifics to advise about any one patient, but the survival data quoted in all of those papers back around the 1990’s to 2000’s is now old data and while MM is still a commonly mortal disease, survival is now generally significantly better than it used to be - even with renal failure as a complication.