If they would have never reversed the 9s in 1935-6 (?) they would have done even more remodelling on that back 9 - now front 9, IMO. They didn't hesitate to have RTJ redo the whole creek-pond-allignment of 16, which in my opinion was massive. They moved 10 green considerably, and certainly lengthened all the tees on the current back 9 along with repositioned bunkers, added rough, planted many trees. So, they did what they thought they had to do to modernize and lengthen as the B&I changed and the length factor and protecting par obstacles changed. While they certainly made changes to the current front 9, I think the changes besides bunker repositioning and length, and narrowing, would have been even more pronounced, had the original 9s been retained.
They wanted it to be a Major, and would then or now do whatever is necessary to grow and cultivate the mystique and cult of the Masters. So, yes I think it would have been a major, no matter what, and it would have been a bit different series of hole designs if the original back 9 was not reversed to the front. Hell, they may have dug 3 more ponds, planted palm trees, and added a waterfall for all we know....