I don't really think that would matter to me. My mage will have control/support abilities, helping the other party members and making the enemies more squishy. Worked just fine in the previous games for me, at least, and I mostly choose based on the characters and not on their classes anyway ;D.
Of course my choices can change if I see any other party members that fit better with my mage character. If I see a cool rogue character (I don't know much about Sera for her to interest me so far), they could take the place of someone, though I'm pretty set on having Varric and Cass in my party, and I love what little I've seen of the Grey Warden bara so far so it would take a lot to change my mind.