In the discussion "Party Members You Always Use" I made some points about Gorion's uselessness (IMO). Which got me to thinking, what was he trying to do? And by extension, what was the Harper's plan?
The prophecies talk about "Gorion's Ward", it's only in TOB you find out that GW is meant to be "the savior" because the alternatives are so much worse. Whether playing good or evil, you are still reckoned to be the best bet.
So, nobody knows about the TOB bit, but they have to be aware of the first. They are also aware of not being allowed to interfere.
So how does this knowledge play out if Sarevok hadn't turned up? Why was Gorion even allowed to enter Candlekeep with you, and Imoen what were they thinking? And why did he ensure you were so woefully unprepared for something that everybody knew was going to happen?
The only plausible reason I can think of is that Gorion and the Harpers were trying to break the prophecy. Prepare a "Gorion's Ward" that was going to be unable to create chaos or take part in any Bhaalspawn Wars because they would be easily killed. I wonder if the letter you find was a last minute attack of guilt on Gorion's part for being a part of a conspiracy to leave you totally unprepared?
Anyway, would like to have people's opinions on how they see it panning out had Sarevok not killed Gorion.