If I have multiple billions at stake, I would assume my broker would be even more demanding of responding within a time frame. Note, I'm not calling for automatic liquidation, but rather some timeframe wherein discussions must be held or else the posted collateral is seized.
The problem there is at that level you're also a significant source of money for both the company and whoever gets bonus/commission on the money you bring in so suddenly there's a lot of reason to not make you annoyed enough to take your business elsewhere.
