.
Some could have new, demonic-seeming bodies, while others could still look normal but be very alien mentally.
The casaulties might be very weird - more something to freak players out than be a serious combat thread. Things like hordes of people with no heads mindlessly mobbing any people who come near them. Animals that have been merged with plants or rocks.
You could also have total new race born in the magic - something along the lines of the beetle headed girls (can't remember name) in Perdido Street Station.
How are those who got left behind going to feel towards returning refugees? This could be a major aspect of the world. Maybe the freaks decide that whoever ran away doesn't get anything back - creating a dichotomy between the overcrowded safe area and the ravaged area where land and supplies are plentiful.
With some of the rifts still open, this could be the basis of a campaign- plane or world hopping as players explore this new system. Some of them might lead to other rifts in other parts of the world, acting as teleportation devices.
Bottom line: people rarely take risks without potential rewards. Why are people venturing out of the safe area? Possibilities:
Overcrowding - food prices have skyrocketed
PCs are all convicted criminals who have been exiled
There are pockets of magical precipitation on the ground that can power magic items.
Portals have been found to planes rich in metals or gems
legends of women transformed into superhot magic babes
The gov has determined that the city and surrounding areas are subsiding into the sea - they need to find new lands before it becomes public knowledge and sets off panic - the fishing fleet has come under military jurisdiction (subsidence is most obvious when you work right at the coast).