Most people will answer, and have been answering that until they're rich or basically set for life they won't sell all of it. However, that doesn't make a whole lot of sense. Why would you put that money in a currency which is guaranteed to go down in the future due to inflation. You're basically putting your money in something which is guaranteed to lose you money. So, Bitcoin or at least another investment is probably the better choice. At least with Bitcoin you've got a currency which was designed to be deflationary. Obviously, there's always the risk of it not quite living up to expectations, depending on what yours are. I imagine when it becomes a little more stable in many years, it'll be a lot more stable, and the money earning opportunities that you have today, will be gone.
In theory if our predictions about bitcoin becoming an universal form of payment, or at least something close to it, become true then it makes no sense to ever sell for fiat, so if we need in the future to use our bitcoin to buy something we want, we should use it directly instead of taking the additional step of selling for fiat first and then buy what we want.
And with how bad fiat is performing at the moment, and how things could get progressively worse, it seems to me that holding a store of value forever makes the most sense.