Paizo said in an interview they are not planing on just updating the existing books and republish them, I am worried that my pawns will not match up with the new bestiaries.
They said they are creating new statblocks for the monsters with new art and new descriptions.
"The monsters will all change" is not at all the same as getting rid of all the old monsters and creating new ones.
It's just that a Hill Giant in the new bestiary will have a new stat block, and the picture will be different and they'll write up the description of hill giants again.
But it does not mean that your old images of Hill Giants can't be used. There are still Hill Giants.
Unless you insist that the hill giant pawns in your game look exactly like the hill giant illustrations in the new bestiary, then you're going to be fine.
To quote Erik Mona: While we've said we're not interested in a product schedule that simply regurgitates all of the P1 books in P2, we absolutely ARE going to have a monster book with orcs and dragons and stuff in there.