OK, I'll bite on this one (which reminds me of the "what would Sammy Wanjiru done if he hadn't died" discussion that got silenced fairly quickly because of the emergence of Kipchoge).
There's more than just times to become the GOAT. There is a level of dominance, a redefining of the event that is more than just times. Its championships and times and a very high profile "rise to the competition" again and again and again that becomes a must-see sporting event.
I've said this before and will continue to: marathons became dominated by "faceless Africans" for years and years - its why World XC, once one of the best events on the athletics calendar, got moved to every other year. They didn't speak english, weren't good at media, just showed up with names that the USA and BBC couldn't pronounce well and then disappeared. Is this a white media bias? Absolutely, but its what happened. And a little of that is also technology: in grainy, 525 scanlines TV sets, you just couldn't see the athletes well with dark skin in shadow or back lit. Once you had HD, you could see just how had it was even for them; how hard they were actually working. And Nike and Adidas didn't even figure out that the pro athlete kits some seasons didn't look good against dark brown skin as opposed to European medium pink. Good job.
Kipchoge became must-see for years. They hyped him up, race after race, and he delivered. When, with the older shoes, the typical elite marathoner's career peak was 2.5 years (as figured out years ago by the Brojos), Kipchoge defied expectations again and again. Winning Berlin with the insoles coming out of his shoes? Epic.
And perfect for the media.
The media has to WANT to love you. You give them eyeballs, something to talk about before during and after, continued content, you can speak well and they will make you a STAR.
So you gotta have everything and Kipchoge had it: the Zen persona, the times, the staged events, the wins and the longevity. That is a rare, rare, rare combination. For his insane excellence at all disciplines, Bekele didn't have it. Track fans know his dominance in XC and track, and how, when he focused, how good he could have been at the marathon. He wasn't the right guy. And had he lived, Wanjiru was clearly not the guy. The times and wins might have been there, but he wouldn't have been advertising products on adverts in Heathrow outside of London Marathon weekend.
So now to Kiptum - this is tough and we will truly never know, but running sub-59 for the second half? Given the incredulity of Asseffa's and Ruth's WRs on the women's side, the questions that Kiptum didn't have to answer, and that Sawe is desperately trying to get ahead of, would certainly have come, as well as the scrutiny. It will always be a massive "What would have happened..."
All I know is that the media will fish around desperately for a Kipchoge replacement, but even if he is Sawe, we won't know that for a few years. Eulid is going to continue to be present in the media, which will continue to cast a long shadow, and Sawe will have to continue winning for at least 3 years at majors and the Olympics and get very, very good at media to have a crack at even being considered the "next up."