Character mistake: When the Terminator scans the doorman at the bar, a display comes up categorizing each piece of the doorman's clothing. The word "briefs" is misspelled "breifs". (00:13:40)
Character mistake: In the opening narration, John Connor says that he was attacked by the T-1000 when he was 13 years old. This is wrong. In Terminator 2, we see that John Connor is only 10 years old, as shown on the police computer when the T-1000 accesses it. (00:02:20)
Answer: He was originally in talks - and by some reports, did appear on set for some period of time. While factual answers are in short supply (for obvious reasons), there appears to be a connection to his drug-use habits. For instance, he was checked into a hospital (LA Cedars Sinai) for what friends feared was a drug overdose in April 2001, and has been in and out of rehab over the years. Chances are the production company was unable or unwilling to get completion insurance.
Rooster of Doom