That part he could believe, more or less. Stood to reason the Sheriff couldn't hold them forever. Either he'd slip and they'd track him back to the house or, eventually, he'd tire of hurting them and just kill 'em all outright, abandon 'em to claw their way back over weeks or months.
(Will's stomach lurched at the memory of all the modes of dispatching the threat of the Sheriff that they'd rejected as too monstrous – and too impermanent, besides. Lock him up and throw away the key. Abandon him on a deserted island. Bury him deep, at the bottom of an abandoned mine shaft. Leave him to die, over and over again, of starvation or suffocation, with only the faintest hope of rescue. If the thought had occurred to them, it must have occurred to the Sheriff. And nothing was too monstrous for him.)
"We'll get 'em back," he agreed slowly, but there was still that heaviness in his voice. "It's the when, that's what eats me. Cos the longer he has them, the worse he can hurt 'em, and for all our looking we've still got fuck-all. Best plan we got at the moment, hell, the only plan we got is to use one of us as bait."