Not necessarily - it could literally be one paragraph or a few lines changed - or Alito elected to let another justice write the opinion. I don’t think if the current position of the Court was substantially different that this would have been leaked, but that is obviously only speculation.
But since it is a draft and not a final opinion, you are right, we have no room to celebrate just yet. Our reading of the case after the oral arguments was that they would probably weave a thread upholding Roe while at the same time finding that the laws that sparked the lawsuit were also constitutional and not strike them down - which would still been a huge step in the right direction. Now if that is what happens after this leak, it would seem like a huge letdown.
Your thinking is sound on this. I would fully expect Roberts, when faced with RVW getting tossed, doing everything he can to form a legal pretzel weave to have it both ways as you suggest. I agree even that would be significant win but far short of what was hoped for when the leak hit.