I think she will forgive him...
In the season 4 finale, I thinks Irina said something like"You are not as covert as you think"...meaning I think Irina knows what he has been up to and she also told Syd that she would see her on her wedding day...therefore it can't be that bad if Irina told Syd that she would see her on her wedding day and the fact that Vaughn is still breathing cause Irina would have killed him if what Vaughn is or was doing is gonna hurt her daughter...oh and she didn't tell Jack did she?...Right?!?!?