After deductibles Orginial Medicare only pays for 80% of medical costs and nonthing for prescriptions. You are responsible to pay the other 20%
The honest answers is yes, you can go broke if you only have Original Medicare. In fact most bankruptcy are caused by medical bills.
A Medicare policy pays the 20% and deductibles you would have to pay out-of-pocket for Original Medicare. Depending on the plan, you may or many not have a co-pay.
If Medicare does not pay, then your Medicare or Supplemental policy will not pay.
What is covered are creditable medical coverage's approved by Medicare.
As long as you use an approved Medicare hospital, clinic, pharmacy, procedure or approved prescription then it's covered.
However, your plan may have a network for in-state service and may be subject to out-of-network costs.