These resignations confirm a fundamental structural problem with the whole leave prospectus: it was a fantasy, and as such incompatible with the mundane fulfilment of ministerial responsibility. Raab has come to the same conclusion that David Davis and Boris Johnson reached earlier in the year: it is easier to be on the team that accuses the prime minister of failing to deliver majestic herds of unicorns than it is to be stuck with a portfolio that requires expertise in unicorn-breeding.
The only possible outcomes were ever basically: "Norway," "no Brexit," or "no deal," with "no deal" actually requiring lots of deals to prevent the island from plunging into the ocean. May's deal is, roughly, a Rube Goldberg version of Norway with some additional kick-the-canning thrown in.