I'm so sorry about your mom's illness. That sounds really scary and I hope she will recover fully and as quickly as possible.
On the health insurance, most policies involve deductibles, which you've identified, and co-pays, which you don't mention. A 20% copay isn't unusual, so in such a case besides the deductible there would be charges (to your mom) of 20% of anything up to that amount, typically up to some additional limit. Having navigated this myself I can tell you that assorted charges you have to pay may not count against the limit, e.g. in my case prescription co-pays didn't "count," I had to pay them, but they weren't included in calculating the amount I had spent so far that year. Tedious (at best). Keep good records, and be sure you have full information about what the policy does/doesn't cover. Don't be afraid to ask questions/challenge charges.
Though your mom's not "old" it may be worth looking into whether there are resources in your community available to seniors that she would be elegible to receive. This kind of thing (and the age cutoffs for the 60+ set) seem to vary a lot by community/state.
Given your parents' ages it is possible that your dad could file for early retirement through Social Security, defer (not collect), but still have your mom be able to collect (likely a small amount, but all the same) on his record, if she cannot return to work. Down the road, it sounds (again, depending on when and whether she can return to work) like she may need to look into purchasing heallth insurance privately. Hopefully as the ACA rolls out that will give her good options.
Depending on her needs and capabilities and their availability and personalities, her helpers may find that technology makes the task less burdensome -- for example a "baby" monitor could make it easier for someone in her home to keep an "ear out' for her without having to be very nearby at all times.
Good luck to you and your mom and dad as you navigate all this.