I own my business can a collection agency garnish me?

Ok my dad had a emergency heart surgery 2 yrs ago making a HUGE hospital bill we've been paying on it each month but being its so much we haven't put a dent in it. So now its at a local collection agency, yes he owns a trucking company but was unable to work for the 1st yr after,he doesn't get a pay check so now the collection agency Is trying to sue him, what can they do bc they can't garish a paycheck when there's not one. And they are unwilling to settle, and I think that if we're willing to pay it off but can't pay the full amount, I've heard of people settling for like cents on the dollar?? Any advice would be appreciated