Is there a significant difference in story flow if the the traitor is discovered, or is it ultimately a minor detail relative to the final confrontation?
I'm considering running this for my group, which just transitioned from EotE to AoR. However, we're in 2 ABY and I saw that this base was destroyed just a few weeks after the Battle of Yavin. I don't mind tweaking canon. However, does anyone know of any important Rebel bases that were destroyed in 2 ABY that this adventured could be reskinned with? I suppose I could also just wait for 3 ABY and the Battle of Hoth.
I can't help you with the second question, beyond suggesting you just retcon the thing since the environment is pretty specific to that base. However, regarding the first....it seems like the reveal of the traitor is a bit of an inevitability. Unless the PCs really screw up the investigation, which they can only do by fingering 2-3 innocent people (which pretty much sabotages the Rebels' trust in the group). That being said, the story doesn't seem to be able to fathom the third act without the traitor being revealed in the second (unless there's a detail I missed, it's been a while since I gave the book a thorough read-through).
Agreed on the timeline point - changing the year of this adventure to 2 years later affects nothing but a line of two of dialogue in boxed text, so it's far easier to change than swapping the entire planet Episode 1 happens on.
Regarding the other point, yes, as written, Episode 3 depends on the PCs finding the traitor (and also on the traitor escaping with a particular hostage) in Episode 2. That said, Episode 2 is structured loosely enough that by triggering the right events and dropping the right hints via NPCs you can nudge the players in the right direction if they're in danger of failing completely. The traitor, incidentally, knows that there's a mole-hunt going on for them, so if the players completely fail you could have the traitor panic and flee anyway. In that case you would want to have some consequences (like maybe having the players' favourite NPC on the base get murdered in the process and make the time limit in Episode 3 tighter). Otherwise I can't see any alternative result to PC failure here other than the traitor leaking the base's location sooner or later, resulting in an Imperial attack on Resolute Base which the Rebels have no hope of winning.