RE:Please READ the prospectus... and the answer is that if you read the prospectus, it also states on page 27 that "Underwriting Agreement means the underwriting agreement dated [BULLET] , 2018 among the Company, AltaGas and the Underwriters."
It's bulleted because the underwriters haven't signed it. What you're reading is a description of the underwriting agreement that will be entered into when the deal is signed and priced (i.e. when they file the ifnal prospectus).
Until then, the underwriters aren't on the hook for anything.