This may be a silly question since I've never been in this kind of situation, but why doesn't the IT staff all collectively refuse to train their outsourced replacements? Or go on strike? Even if they aren't unionized, they could go on strike (I assume). Am I just making some bad assumptions here?
Two main reasons - One of the conditions of getting a half-decent severance package will be that you have to train the outsourced labor to a standard satisfactory to the remaining management; secondly, one of the unwritten but impossible to avoid/prove conditions of getting a good reference from the employer will be training the replacement.
So... refuse to play nice with the managers screwing you over like this? No problem, you're fired immediately and you will get no reference from the employer (or even worse, an "off-the-record" conversation between your old manager and a potential new employer saying that they were happy to get rid of you because you are not a team player, have a bad attendance/disciplinary record, poor standards, racist views, take regular holidays in the MIddle East, and take regular breaks every hour or so to pray to Allah.
For the small minority who have enough money in the bank to get them through a lean year, or who get head-hunted, it is deeply satisfying to play the clown for a week while "training" the new hire then walking into the manager's office and taking a crap on his expensive chair. For the vast majority, though, who have the kind of personal finances that most members of the consumer society have, that severance package is badly needed and should just about cover the basics.