Having had a family member suffer from kidney disease, I can say just what an enormous (positive) difference a transplant (two in the end, actually) made to his life - so I really do wish you well, and I hope this works out for you. That is the overriding thing to be happy about.

In your position I would certainly strive to reach Gold so you have the guarantee of a soft landing to Silver. You have nothing to lose in asking, BA are quite compassionate in these circumstances, but my inclination would be to say that the odds are probably against you being afforded some discretion given you have no history as Gold and not that much as Silver.

Had you been a very high value customer, maybe GGL with lots of BA metal travel, or at least a multi-year Gold then maybe your chances would have increased. I certainly wouldn't ask the question until you reach Gold and your status is confirmed - the Gold line has generally more experienced operators who may have a better idea where to turn.