None of this years recruits are signed yet so they can still choose to go elsewhere. As for everyone already enrolled at Houston, they knew Herman was probably gone this year or next year when they committed and signed.
Also, the kids coming back for Houston will likely still have a great team, particularly for their conference.
Houston has only made one so-so hire in the past fifteen years.
They went from Briles, to Sumlin, then a 21 - 17 "down period" with Tony Levine, and then Herman.
Three of those coaches ended up with pretty good jobs.
Houston will hire another very good up and coming coach. They'll probably win their conference next year and the countdown to when their new coach leaves will start.