Agree with the others. If no issue with the exterior of the batteries, very likely nothing leaked out. I'd say re-wash the sheets just in case, and indeed chuck the batteries. I'd think even if something did leak out, 1) you'd likely see staining, and 2) it would be OK with another wash. EDIT: and I don't think anything bad would happen to the washer either, FWIW.
Oh, and switch to AC-powered Magic Fingers