i have mixed feelings about this. i LOVE Lena Olin, i'm a huge fan and i will support her no matter what she decides. but i'm also crazy about Irina and i would hate to see the character killed off.
i think the problem with re-casting is that for 3 years now the only image we have of Irina is the one Lena gave us. any other actress who would take her place, no matter how talented she is, will have a hard time competing with that. Lena played the role so well, you'd think it was written for her. so anyone who is gonna replace her is just not gonna be as good. which is why i'm totally against re-casting, in addition to the fact that i still hope Lena will come back next season.
i know that a lot of us are missing Irina and that IMing is just not the same but at least when they mention her on the show or when Jack contacts her, we instantly see Lena in our mind's eye. so in the end, if there is absolutely NO WAY Lena will EVER come back to Alias, then i'd rather see the character killed off instead of recast.