In what way do companies have an economic interest to have healthier employees?
Heck, in the US they can even just fire them when they get sick.
Well, they could, yes. But wouldn't company counsel advise them to just settle the inevitable lawsuit? (Serious question, BTW; not like this IANAL follows the case law.)
There are a couple problems with this:
1) It's only for fairly serious conditions. If it's just "I feel like crap all the time because I've been stressed out for years" then in most states they can fire you.
2) It's unclear to me (IANAL as well) if they are required to extend non-pay benefits to you in that time, but I think not. So if they do not extend health insurance to you in that time, then you might be able to come back, but you'll be bankrupt.
Some companies self insure and only have the insurance company handle the billing. This provides arm's length from employee's confidential health care.