oh dear
If you go into debt, you will be charged a 5% penalty each week until you are positive again at the time of a economic update. If your account is below -$500,000 at the time of a weekly economic update, you are given two weeks to bring your account back above -$500,000 for an economic update before your key players will be put on the transfer list automatically with a starting price of $0
thats straight from the manual - which suggests that if next financial update you above above -$500k, then the counter resets.
so technically speaking it sounds like you could tic-tac between above and below -$500k for weeks and still be ok.