Have been reading a history of the 70s lately, fascinating stuff, and much of it seemed very, very familiar right now. ('Worst economic crisis since the war' / 'We have to share the pain' / etc)
Interesting point which I had forgotten from the late 70s crisis when the IMF was called in, massive cuts had to be agreed on etc. Crisis was based on Treasury estimates for the PSBR. When the true figures came through, the actual PSBR was less than half the estimate, and indeed very little of the IMF loan was actually called in.
The author interviewed various treasury civil service bods from the time - and got a very telling quote, saying, essentially, that there is only an opportunity once every 10-20 years for the Treasury to really slam down on spending, so whenever they see the chance, they make the most of it.
IMO the whole scenario fits very closely with the current situation - and again, the opportunity for a one-off reining in of public spending is clearly being taken.
Regarding the OP - 'what happens when the deficit is paid off' - do you know the John Donne poem, can't remember his dates exactly, but maybe 1650s?
'As Princes do in times of action get
New taxes and remit them not in peace . . .'
I guess not much changes 