I'm going to essentially echo /u/marisacoulter here and say that we cannot meaningfully answer this. Part of it is the imprecision of Soviet records, but additionally is the problem generated by what records we do have. If you look at this chart showing strength and losses by Quarter, taken from "When Titans Clashed", you can see how in the early period of the war, the turnover in the Soviet military was massive. But that is still looking at three month periods, so it doesn't account for the changes, literally every day, in personnel, which means any numbers we attempt to calculate there are still not telling us very much about reality. Different roles affect chances to make it, veterans are know the tricks that neophytes don't to avoid the worst, and more simply, that 'strength' number is a 3 month average. You would need daily exact numbers (which don't exist) for a perfect percentage. Or, that is to say, if you calculated the percentage losses of each quarter, and then calculated the survival for every quarter of the war based on that percent, it wouldn't actually be the answer. What we can say is that while he is hardly alone, but unless someone were both able, and willing, to access individual service records for every soldier than we can't know just how large a cadre he is a member of, and no study like that has ever been done (nor is it possible given a lack of perfect record keeping). We know of others, from memoirs, and the like, but nothing institutional.

I've covered some of the issues here, but I would also point you to /u/flobota's answer here which while for WWI, brings up some great points on this issue, broadly.

Statistics on survival are difficult to compile, as the Soviet Union did not like to admit how many losses they suffered. I have a question, rather than an answer-- does your grandfather have any documents from his time in the war? Any letters, drawings, things like that? An AMA is a very interesting idea, and I encourage it, but as a historian I would also be very interested to know about documents he has.