Every time you buy, the market price goes up. No matter how rich you are, there is no such thing a s a single order suddenly getting all the available coins instantly.

Therefore, the whale will always run out of funds because of his own action. So no, this cannot happen, even if they band together and try, they simply cannot buy all the remaining bitcoins. Besides, most bitcoins are being kept as savings ("hodl"), only a minor amount is in the market.

This is also the same reason why printing money to buy all bitcoin is not possible, it will simply crash whatever fiat is used for that.

I hope you now understand one of the reasons bitcoin is so valuable to their holders...