You will drop to Preferred status - with a max of 8 chars (?) per server and access to all the story content (Level 70 etc if the sub ends after 2nd Dec)
a credit limit of 350k per character, 2 crafting skills, limited (or no) access to Heroic loot, FP loot, PvP & Ops etc
https://help.ea.com/en-us/help/star-wars/star-wars-the-old-republic/swtor-free-to-play-faqs
http://dulfy.net/2012/10/24/swtor-free-to-play-ftp-player-restrictions/