I wouldnt worry but Id Keep my eye on the IAH-JFK Inbound and be ready to go LGA-IAH instead, of cause youd also have to keep track of the avaiolable seats LGA-IAH. I guess if your Gold or Plat you can always pay the $25 for confirmed SBY and know 100% your flying out of LGA 12 hrs before your flight time. I do believe CO will allow LGA & JFK to be switched w/o any problems, chance of remaining up front probably Nil, but then again chance of having to overnight it @ IAH also Nil