The shortest of answers, issued in my capacity as a Board Certified Specialist in Creditors Rights Law:
a) Guitar Denter is in Chapter 11 reorganization. It is not in Chapter 7 liquidation. The aim is to stay open, jam some creditors, maybe close some stores and maybe not, and get out of bankruptcy as quickly as they can. That's not the only possible outcome but it's the most likely.
b) They're open. In terms of national online sales, have at it. As for the store you drive past, if you want it to stay open stop in and buy stuff.