You can't solve the problem with only partial foreknowledge. Being required to continue to pay redundant employees is a cost whether you know about it ahead of time or not. And not hiring employees you're not sure if you'll need is a catch-22. If you hire them and don't need them you're screwed, and if you need them but didn't hire them you're also screwed. Which one is the "bad decision" at the point in time when you don't know whether you'll need them or not?

The solution is for employees to negotiate their employment contracts. If you want X months of notice before being terminated, demand that it's in your contract before you agree to work there. But that will mean the employer will want to offer less compensation, because they're incurring a cost and it's always a quid pro quo. Putting the rules in the law instead of the contract only prevents you from choosing the other thing -- lots of people would rather get paid more than have more notice when being laid off.

>They'd take it into account when deciding if they could afford to hire them.

Sounds like a great way to incentivise companies to discriminate against old people and people with preexisting conditions.