First of all it's not debt - it's equity. It's perpetual pref and they could suspend the dividend ...well perpetually. The interest rate goes up on the pref after 4 quarters of missed dividends and the pref gets to vote and has some rights. The pref would need to be paid before stockholders if the company is sold, goes bankrupt (both common and pref would be wiped out) or wants to pay a dividend on the common (which won't happen any time soon even if there weren't debt covenants against it).
Check out EMMSP as an example of a similar pref issue where the dividend has been suspended for many years and won't be paid anytime soon.