Well, you don't technically need a living navigator to go through the Mycelial network - that much was established in season 1.
They did mention that their computer systems aren't advanced enough to produce a synthetic version of a living brain because of some ridiculous notion that biological life is somehow 'special' in comparison (whereas in fact, its not).
All you need is sufficiently advanced computer (such as an AI). -which Federation computers were perfectly capable of in the mid 23rd century - its just the writers like to make 'biological life' 'mysterious' and 'special' without realizing that computers and algorithms ALREADY surpassed Humans in virtually everything (even creativity is nothing special than a random dataset a person was exposed to throughout their life and then connected it based on their own preferences and experiences depending on the environment they grew up in - an AI or algorithms in comparison would have a massive database of information at their disposal, far surpassing anything a human could learn at any point in time, and can access it and/or find patterns in less than a second, vs a human who needs days or more to do the same).
Control's motivations for destroying all life never made sense. That's just writers saying 'AI is evil/dangerous because we say so, and we don't know anything about actual science or technology, let alone neuroscience or how behavior emerges - so, we just go with what we think will 'sell').
Even with Control neutralized, do we know for certain that all vestiges of it got removed?
Some aspects of it might have survived in a different form.
If it got its hands on the spore drive, it could probably use its own knowledge to extrapolate what Discovery was up to and that there could be a vast repository of data in its databanks... although for the life of me, I don't understand WHY would it need it considering the Federation database is ridiculously large as is and would give an AI a heck of a starting point to become 'unbeatable' (if that's one of its goals) and could come up with breakthroughs in seconds vs carbon based lifeforms.
Why destroy life in the galaxy?
What possible purpose would that serve? Self-preservation? That's assuming all biological life would want to eliminate it.The universe is ridiculously big in comparison and there would be little to no point in doing so.