Getting you insurance to pay for inpatient recovery?

Specifically if they have never paid for outpatient? I'd rather not show up to the emergency room, but I'm at the very edge here and outpatient isn't going to work for me. I've contacted a few rehabs and some will not assess me until I've paid large non-refundable deposits. Those places are obviously out.

A couple places have done over the phone assessments and are working with my insurance (which thankful doesn't totally suck).

I just really don't want to be half way thru hard work (dual diagnosis) and either get booted or stuck with an enormous bill. that would be awful for me.