system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] What if the Genophage had failed and everyone's worst fears about the Krogan had been realized?

Say the Reapers showed up to find a Universe entirely populated by sub-sapient life forms and Krogan.  Even the Geth have long since been stomped under webbed feet.

What then?

Or what if the Krogan managed to sterilize all habitable planets via ruinous nuclear warfare ala what they did to their home planet?
gpt
The cycle itself would have been extended, Sovereign would have taken a look at the current status of the cycle and come to the conclusion that action need not be taken - yet.

The krogan aren't a dumb race. They've got incredible minds like Droyas and Okeer, respectively. But they're no Mordin and you won't find many, if at all, setting up facilities on Noveria.

First Contact War with the Turians would not have happened and the Skyllian Blitz can be struck from the books, too.

I don't recall how the First Contact war ended, but it ended well, for both the Turians and Humans, in that both races came out virtually unscathed.

With the Turians being ground into dust by Krogan onslaught, Humanity would have encountered Krogan vessels.

All down hill from there for humanity.