I seriously doubt you'll see insurance companies pull out of Texas. If they haven't after some of the hurricane's and tornadoes we've had hit the state in the past...I don't see them doing it now.
Why would they?
They will reassess the low lying area risks and raise rates some, but Harvey will be salesman of the year when this is over.
People well above 500 year flood plains will be seeking insurance after having been bit this time, and that will mean a far larger pool of insureds, some of which will be low risk in an actuarial sense.
It was an
unprecedented set of circumstances (blocked by two high pressure systems) that stalled the storm on the coast where it could gather moisture and energy and dump that on land, without moving through.
Those who got hit hard this time will be seeking policies as well, so I expect that when things are more normal, there will be a bigger market for insurance than ever.