I think that IB ist one of the safest places at the moment.
First, IB ist still largely a private company, so no risk of irresponsible behavior of CEOs which are not owners.
Second, Petterfy ist a veteran in the options business. If there is one person who knows how to measure and avoid risks, he is.
According to their website, funds are held at various banks, selected depending on counterparty risk. I have no reason the question this statement at the moment.
IB has been critizized multiple times for their very conservative, risk-averse policy (for example, suspension of intraday margins during high volatility periods). Most people don't seem to understand, that exactly this policy is in the best interest of their customers in times like these. Better be safe than sorry.
Conclusion: IB may be in fact one of the 'safest havens' existing at the moment.