My thought on the "if the business works" case is that such employees should have a clean path to either transition to the company they helped make a success, or get reassigned by YC. Either one is a win for YC in this scenario: An employee which helped a startup succeed is a hot commodity they'd love to reuse, but they also own a portion of the successful startup, so having it continue to succeed is also a big win.

The idea here would not be for YC to have a constantly growing outsourcing team, but to ensure they didn't lose the good employees because a startup failed. In a given failed startup, there are likely some rockstar employees that definitely weren't why it failed, and it's in YC's best interest, presumably, to hang onto those great employees and get them placed with other investments of theirs, should the opportunity arise.