So what's in store for the fifth season? ABC has released an official synopsis: "After they [Sydney and Vaughn] both survive the car crash, she learns that the man she has known as Michael Vaughn is under investigation and suspected of being a double agent. She questions whether their business and personal relationship over the years had all been a lie. When Sydney discovers that she is pregnant with Vaughn's baby, she is determined to uncover the truth about him.

Meanwhile, because of Jack's past betrayal by Irina, he begins to worry that his daughter may suffer the same fate as he did. He will also have to deal with the fact that he will soon become a grandfather - while still learning how to be a dad. Sloane will have to do some soul-searching of his own, as he makes an unholy alliance in his desperate fight to find a cure for Nadia - who is still in a coma. New agents will be introduced and a nefarious organization will come to light in Sydney's life as she fights to protect her unborn child -- all the while traveling incognito, outsmarting the bad guys and keeping the world safe."

Michael Vartan is out. This was rumoured for a while and basically denied. This is being reported in a number of places now though.

From eonline:

Parting Is Such Sweet Sorrow... Heartbroken. Shell-shocked. And just, well, sad. I've never approached a column feeling quite like this, which explains why I rewrote this paragraph nine times before I realized there's no easy way to say:

Someone is leaving Alias. A main, integral character.

It's happening early in the season. And many of you will be devastated.

Now, I'm sure some of you will hate me for this, but I'm not going to name this person. For the sake of the fans (and you know I'm the biggest) and for the sake of those who work so hard on this show, I can't bring myself to ruin what is sure to be a fantastic, mind-blowing twist--the very reason we so love Alias in the first place.

To this end, I've actually sat on this for a while now, and I planned on keeping it a secret. So, why am I opening my big fat yapper now? Because, over the past few days, it's become evident the word is out. Not only has my trusty Batphone sirened five times from different sources telling me the exact same news about this actor's departure, I know reporters at weekly magazines who are thisclose to breaking it.

It's coming.

That said, as the show's biggest cheerleader and the first card-carrying member of Aliasaholics Anonymous, I feel compelled to prep you with an early (and hopefully, helpful) forewarning, along with a request to keep in mind two things when you do hear the news.

Leaving by Choice: Whatever salacious spin these mags may put on this person's exit, the truth is, this AWOL Alias star is leaving of his/her own will. So, let's try to keep the bitter rage to a minimum, mmm-kay?

Just had a long chat with a trusted Alias source who gave me a different take on the situation with the AWOLAS (AWOL Alias star).

According to this source, this departure actually may not have been at this person's request. I'm told s/he was informed s/he would be leaving the show for creative reasons ... that the character had run its course.

I find that, um, shocking, if true.

No. Greg Grunberg is out, by his own choice because he feels his character has run it's course creatively. He wants to go back to doing comedy.

Yes Grunberg is out and he has gone public with this and it is of his own choosing. Vartan is out as well, early in the season, but not of his own choosing.

actually, you're article specifically DOES NOT name anybody so I fail to see how you can be so certain it is Vartan since as you also pointed out, that particular rumour has been outright denied. For all we know it could be sloane, or far more likely: Dixon since they haven't figured out what to do with him since "Phase One"

The article I posted didn't mention any names, but there are a number that do. Eonline has an article from Ted Casablanca specifically mentioning Vartan.

One of the clues given on the site said that the actor was "broadsided", no doubt a reference to the end of the season