Power word stun does seem pretty bad if it does nothing vs people with more than 90 hp. It seems hard to justify vs attacking 16 times a round with his bow but idk shit about 2e.
I'm not sure how the blink works on the dagger. If its just whenever they attack then its not that big of a deal but if he also gets blink as per the spell then the rouge is kinda rolling at advantage because if either the blink timing or the rouges normal initiative goes before Imirik's the wording of the spell make it seem like it'll cause the spell to fizzle.
I find it hard to believe that they will be able to win the fight without at least being hit by this rouge at least once. It seems like blink is also gonna stop second attacks at the end of the round. They might want to consider leaving there enchanted armors at home but it also kind of sounds like if they get hit there just dead so idk.