Those are very good questions.
When it comes to older displaced workers particularly, the time horizon that exists in order to recoup the initial cost of retraining is relatively short. That's one of the reasons why retraining for another occupation might not be the ideal policy response in the case of an older displaced worker.
The research has tended to show that job retraining programs suffer from a lot of design flaws, perhaps, in that when they're done outside of the apprenticeship model, where there really might be a vacancy for the worker down the road, it's kind of a hit-or-miss operation.
I think the evidence is suggesting that what does pay off more than trying to retrain someone for a specific occupation is to retrain them in bolstering their more generally applicable skills of literacy, numeracy, and document use, perhaps with a year at a community college or something like that. That's a good way to help them learn how to learn, and how to be trained for, a new job, and the skills when the new job comes up.