For such huge market cap of bitcoin it is just a small percentage of its part . The sudden sell off will surely affect the price by some means for some time but that process will not be durable and will not last long . Bitcoin is going to cover it and has already covered it by its current price of 9,217.98 US Dollar .
Yes, it's a big amount compared to Bitcoin's daily trading volume which is $6-$7 Billion USD these days. If that amount was sold in one day the price would drop more than 50%, but knowing this they will never try to sell it in one day, because they don't want to sell their coins cheap. You are right that technically the price recovering shouldn't take long even if they sod all in one day, but the thing is that a huge sell like that might trigger a panic selling the consequences of which are unpredictable.