More likely you would implement a strategy to sell off a little bit every day. It would take some time to liquidate it all at the best possible price. This isn't any different than the problem faced by any wealthy person with a large position in a publicly traded company would face. You can't market sell 300 million of anything in an instant and not more the price. Bitcoin also has private markets where high touch trading desks match large sellers with large buyer so it is conceivable you could use something like that as well to get a good price and exit your position relatively quickly.
That said if you you are the person who had the vision and stomach to hold that position all that time it's unlikely you would find yourself wanting to sell it all in an instant just because the price crosses 3k. You almost certainly believe 5 figure Bitcoin is possible if not likely and a 6 figure Bitcoin price isn't out of the question. I could seem a person in that position selling a bit to make life comfortable but not panic exiting their position entirely.