While I agree that the placement of the logout link is a little odd, I can't agree that bringing back the user menu is the best solution.
Let me walk you through how we came get rid of the user menu, by examining the items found in that menu:
"activity" link: Specific to you, linked to a tab on your profile page that contains answers you've accepted; questions, answers, and comments you've posted; badges you've earned; edits and reviews you've completed; and edits you've suggested. Of these, the only item that is something that happened to you (as opposed to something you did) is badges earned. We felt that these deserved better visibility and are now in the "achievements" dropdown (along with rep changes and privileges earned). Everything else is just reference; since your whole user card in the top bar links to your profile, you can still access the other information, though it's an extra click away.
"privileges" link: NOT specific to you; a standard reference page that lists all of the privileges for the site you're on. The primary interesting thing about privileges is earning them, which you are notified of through the achievements dropdown. Few people need or want to reference a privilege they don't have yet, so this link went away.
UTC time: NOT specific to you. This mostly matters with respect to the rep cap and to earning badges, so we moved it to the achievements dropdown, where you can view it in the context of those two things.
reputation earned, and recent badges earned: A primary point of interest for most users; we made it more obvious by giving you realtime notifications and a top-level indicator that's not cluttered up with a lot of other notifications (like in the old "notifications" tab of the multicollider).
votes cast, revisions, and changes to favorite questions: Items that are kind of useful, but mostly interesting to a small percentage of power users. (Most users don't run into the daily voting limit, or make many revisions, or have many favorites.) Since they're rarely used, we removed them from the top bar; you can still get to them on your profile.
log out: A user activity. It does make sense to have this near a username/avatar like many other sites have. HOWEVER....
We're at the end of the list of items in the user menu, and the only things that are really justifiable to have there are a link to the profile and the logout link. We know that users want to visit their profile far more often than they want to log out, so making the avatar a dropdown with "profile" and "logout" links is a net loss; it adds an extra click for a very frequently used action. I don't have numbers offhand, but the vast majority of our users only rarely log out of our sites. Obviously, we aren't going to take away the functionality entirely, but I can't come up with a compelling argument to give top bar real estate to an action that's rarely used, or to create a new dropdown that yes, provides a more logical location for the logout action, but which also makes the more common action more difficult.
The placement is a little illogical at first, but it's not impossible to find, and once you find it, you know where to find it in the future. I was worried that it would be a huge pain point for our users, but we haven't seen a significant uptick in support requests on this issue, which leads me to conclude that users either aren't interested in logging out, or they are finding the link just fine on their own.
If you have a better suggestion for where to put the log out link, please post it; I'm afraid I'm not convinced that anything posted here so far is a better alternative, though.