O.K., Marc has posted a lot of shit on that page, but for once I have to defend him. He actually kept it ambiguous, his post was:
Seems she was just in hiding. Janeway is back. Or is she? Find out by picking up The Eternal Tide now available for your reading pleasure.
That isn't anymore definitive than having her on the cover.
(Disclaimer: Just assuming he hasn't deleted a more spoilerish post. ETA:
Although that seems to be a strong possibility looking at the time of KingDaniel's post and the post date of the post I quoted above)