I would have to disagree regarding "every time". I've been doing these for a while now (buying/fixing "water in oil" engines) , and haven't had one go down again once the issue has been dealt with and is no longer leaking water into the oil. Maybe 30 of them? The majority seem to go on living healthy lives afterward.
That's NOT to say the water/oil mix can't destroy an engine if not dealt with right away. I would NOT try to finish up a season for instance. My point is that it's not an automatic full rebuild, including pump, not in my experience anyway. If you fix the leak and it runs without knocking, you're good to go. I've done just 2 that did knock when making a lot of power (starting at near wide open throttle), resulting in a new set of rod and main bearings. I was pretty surprised that the knock on these motors wasn't a lot worse. On inspection, it looked like they could have thrown a rod at any minute! -Al