Thoughts on your thoughts:
-RIGHT! Totally forgot about how Vitiate was behind all this. Kinda the "Apex Sith" in this whole affair. 
-Yes, I agree. I was SO excited when Bioware released the SoR expansion and then I read through the plot online and I just shuddered. Revan would NEVER do a lot of the things he did in that storyline. 
-Ohhh, gotcha. I played through about 11 chapters of KOTFE, but never got to the point where Vitiate revealed that he was trying to use the Outlander as his new avatar. So my question is: how is Vano going to find them? Will she disappear from the Qyaari academy altogether and teleported somehow? Will she have already gotten on a ship and was on her way to Zakuul? 

So basically our plotline would go something like:
-Go find Meetra at this remote base. 
-Arcann and Vaylin intercept, battle ensues. 
-From there...well, does Vitiate somehow intervene through Vano? Or some other way? Renso could communicate with multiple people, so I assume Vitiate (who surpasses Renso in power) could do the same and potentially give one of our party members extra power to give Arcann/Vaylin the creeps? Or could Vitiate possess Arcann AND Vaylin?
-In either case, Meetra dies here. How? I don't know if Arcann would willingly kill Meetra due to the powerful bargaining chip she is, but Vaylin is just cooky enough to do it in order to spite Revan and his gang of upstarts. If Vitiate possesses Vaylin/Arcann, then he could kill Meetra in order to get Revan off-balance enough to do something headstrong or foolish. 
-The party manages to evacuate without Meetra and Yerbol will...well, let's just say he'll be changed from this encounter for a while (I can't give it away xD). 

After that, we can start to piece together how to stop Vitiate. I'd be ok trying to find a solution other than Vitiate's father, seeing as I kinda feel like we've hit our limit on finding older and more powerful beings to fight the slightly younger, older more powerful beings xD