They would never have let Jason run with his concept of Moiraine's trailer for the book if that were the case. He even commented in the making-of that it was kind of a spoiler, but that to his surprise they agreed.

They would never have asked Sweet to put the Tower of Ghenjei scene on the cover if the rescue doesn't happen in TOM (that'd be both cruel and really stupid of them).

Brandon has also hinted pretty heavily, and long ago, that "the big moment" wouldn't have to wait for the second book. He knew this wouldn't please a lot of people impatient to get there, so he prepared fans for this since 2008...

It makes no sense altogether that they are flirting with spoilers to market the book (because Moiraine's rescue is such as iconic, long-awaited moment, they didn't resist) using Moiraine and the ToG, and this turns out not to be happening in the book. They'd have to be complete morons to do something like that. About every review of TOM would end up commenting on the fact the book didn't deliver on the promise of the cover art and all the hints that it was the book in which Moiraine came back.

No only Moiraine will be back, but she'll be part of the reunion of the "EOTW cast" at the end of TOM.