Some things that would help make routes more viable from Dundee would be competitive landing charges, competitive fuel prices and a reduction or abolition of APD. The first of these would require increased subsidies (as would the second in all likelihood) and the last would need a YES vote next September.
If enough passengers can be encouraged to use Dundee airport then perhaps it has a future. The problem for now is that the overheads are being spread across too few flights and too few passengers and the vicious circle is getting worse instead of better.
If HIAL and/or Dundee Council and/or the Scottish Parliament decide that it's worth having another punt at trying to get a decent selection of commercial flights to use Dundee airport there would need to be a sensible business case to support this and then the people and businesses of Dundee would need to respond by using the services provided in order to make them viable for the operators. It will be a case of use it or lose it. In today's climate however it's difficult to see who will be prepared to take these risks.