Then they'd probably look a little like these stereotypical 80s/90s characters, which are illustrated by the ever-talented Mike Wrobel.
Why these characters, and not other, more iconic ones? Well, this set of Game of Thrones characters are just a few in a long series of illustrations in this same spirit. You can see earlier characters here and here, and I suspect, given the huge cast, we'll probably get a few more sets. For now we have Robb Stark, his wife Talisa Maegyr, Bran, White Walkers (!), the Hound, Ygritte, and Twin Lannister. Enjoy!
Side note: some of the cast probably was born in the 90s and may have even dressed like this! Not everyone, though.
GAME OF THRONES 80/90s ERA CHARACTERS (Part 10) [Moshi-Kun]