I think, regardless of the system, that government debt represents additional money injected into the system. Even if the gov did not actually hand out its negative balance to the recipients yet, those can still say ´hey, it´s the nation itself owing me - you can trust me, i will be able to pay soon´, when trying to buy stuff, and thus monetise the debt.
From the game-play perspective, the events could work as ´warning shots´ to approaching bancruptcy. Because, once the guy the debt-holder wants to buy stuff from with the debt gets denied (´uh, you mean that nation, that has like a gazzilion in debts already? No, thanks.´)... well, that´s when you are bancrupt, basically. But as long as this doesnt happen, gov-debt is extra-money inserted, IRL as in game, since the loan-checks of state-employées are still being paid.
If your in-game government is a million in the minus, that means, that you created a million out of nowhere and passed it on to your ´subjects´. That extra million in currency would simply not exist without the debt. On the level of abstraction of the game, it is simply ´extra-money´ and what, if not that, should cause inflation?
The thought crossed me, that it could apply to the other end of the scale as well: If you stockpile money. But that is actually money taken out of circulation, hence not effective, and if anything should cause deflation. Only if too much of it is spent in too short a time, it could cause the contrary, i postulate...
So maybe it should be that: Money spent per time. Anyone remember the global warming meter of Civ1? Something like that would be neat. If you spent too much too fast it goes from green to yellow, then to red with increasing chances of inflation. If you spent too little, it goes the opposite direction and ´below zero´ changes form (say from circle to rectangle) and again from green to red with increased chance of deflation. Both events are bad, generally speaking, so you´d want to avoid them both and thus ´zerging´ (I hope the term kind of fits and you get what i mean) is discouraged. You´d want to spend the same this year as last, at least by order of magnitude, each year, roughly.