can a retailer demand rebates from his suppiers or be threatened with delisting

Yes.  It is not an uncommon practice for retailers with a great deal of clout (i.e. those that have a great number of outlets and thus order in large quantities) to demand rebates from suppliers on items which haven't sold as well as hoped.  While the retailers can't force suppliers to give rebates, suppliers often agree because they are afraid of losing the retailer's future business if they  do not agree to the rebates.