In my experience, on line check in will still work, but you will not able to get a boarding pass. So you will still need to go to the check in desk where they will look at your documentation. Does not make a lot of difference if - through class of travel or status - you can choose your seats when booking, but otherwise (mainly Y for non-status passengers), you can choose your seat at OLCI at T-48 and then get your BP at the desk.