It becomes sustainable by living within our means. Even first time relegation in 20th place brings in £170m which as long as we don't spend £70m now on transfers and wages will start repaying TB OR leave a nice nest egg to subsidise/reduce future losses for mounting another promotion challenge.
I've been mulling this quandary over since they started playing Wolf of Wall St up at the McAlpine and a thought occurred.
They were starting from a very low cost base (someone less lazy than I will know how to find this out) and therefore to walk into £170-190m windfall really is just that...