Not continuing the role of Indiana Jones will be wrong. If there is a fifth from GL, SS and HF, I don't expect it to be much better than CS. I'd like to be proven wrong on that account. This is all just wishful thinking, but i wish George would permit a reboot with a younger actor to get some good stories out of the 1920s and 1930s and that a team with the balls that they had back in the 1980s would make the new flicks.
Comparing the situation to Rocky is not right. The difference is that people will not want to see movie after movie of Rocky getting his head pummeled. I mean, how many different stories can you get out of that anyway?! The world of Indiana Jones, though, has so much potential for many more fantastic adventures without getting stale. Because the world of Indiana Jones is bound up in history, adventure and questing, the sky is the limit.
But I know, you are talking about the replacement of the lead character and thus possibly destroying (or otherwise) the legacy. Again, I don't think the role has been made so sacred by Harry that someone else couldn't do it and do it well AND have it accepted by the viewing audience. I can't see a single reason why it wouldn't work.
I think Harry is almost too old now to do another one without that impacting negatively on the legacy. If what I propose became manifest, we would have the same loved character back to please more young audiences with someone who can realistically be an adventuring and womanising rogue such as we had in the 1980s.
I'd like to actually hear why Harry can't be replaced. No one has given a reason. They've given poor analogies, but no real reason that explains anything other than their emotional attachment to Harrison, which I can understand but would not want to limit myself to.