Frustratingly both The Abyss and True Lies have already been mastered in high definition for blu-ray release but are still awaiting final approval from Cameron. He's apparently been too busy working on Avatar sequels and adding 3D and new cgi effects to the latest version of T2 (coming to blu-ray later this year).
As regards Terminator 2, I've seen screenshots which show that he has used cgi to add Schwarzenegger's face onto shots with motorcycle stunt doubles and has even used it on a shot where the chasing sewer truck originally lost it's windows. Examples:
Terminator 2 : Screenshot Comparison Terminator 2 : Screenshot Comparison
Not really sure how I feel about modern cgi changes being made to T2. Undecided as to whether it's a plus or negative - imo there's a certain charm to an original "warts and all" presentation.