Or the Protostar or Dauntless could leave a standard warning buoy. Or send an email to Starfleet. Or a message explaining the mess. That’s the beauty of time travel. It really wouldn’t be that hard to stop First Contact unless it’s an accident or something.
I already thought about that.
The problem lies in the ship's software (and some other things).
How do we know a copy of the Diviner software isn't sent out every time a ship establishes communications with someone and would ONLY affect Starfleet's ships if it gets in contact with them.
That STILL however didn't explain why Dal hadn't tried contacting Starfleet when Zero showed them that they have an option to either go to Starfleet or back to Tars Lamora.
Dal could have still implemented the plan and send a message to Starfleet explaining the situation - but we don't know if such a message would enact Diviner's plan in action to begin with.
Holo Janeway portrayed the situation before that contacting Starfleet was possible/an option.
So that's a possible plot hole.
Another potential issue is that the Diviner said to Gwyn on the holodeck to help him ARM the weapon.
What I got from this was that the weapon wasn't armed right now and that even if the Protostar comes into contact with another SF ship, the software wouldn't be transmitted or do what it was supposed to do... but then Gwyn backtracked and just perceived that no contact is the only option.
Obvioulsy, with Gwyn losing her memory, it will be interesting to see how the kids/crew realize they have a dangerous piece of software onboard (and one possible option would be that the Dauntless will potentially come close to the Protostar, but then the software will TRY to self-activate - this is how the kids could discover its function and then choose to run away from the Dauntless instead (creating a perception for the Dauntless crew that they are thieves - and sensors would obviously show them SF crew is not manning the Protostar - and with communications being out of the question, well, that creates a problem).
I wonder though if the kids/crew could create a separate message buoy and record a message using 'clean' SF equipment that didn't contain the code and leave the buoy for the Dauntless to find and read - which again would depend on how widespread the Vau'ka'Nat code in the Protostar is.
EDIT: One possible solution to this conundrum would be to say that the code has infiltrated every ship system and that even composing a message and leave it as a warning beacon wouldn't work because a copy of the code would automatically find itself there.
Though this could be potentially circumvented by creating an EMPTY bouy (aka no pre-installed software)... and program it externally with Zero, Gwyn's and Rokh's help (while simultaneously preventing it from connecting with the ship systems - which would prevent the Diviner code from infiltrating it.
That way, the kids could leave a 'clean'/safe message for Dauntless... but there's no reason to think that this would convince Admiral Janeway or her crew - actually, it would be great if things DID turn out this way, and Admiral Janeway decided she wouldn't just go on a word of a few kids who are controlling a SF ship and still decided in pursuing them, thinking that what the kids said was a lie.