ah, but no one stated or calculated the 'probability' as asked. As per wikipedia: Probability is a measure of the expectation that an event will occur or a statement is true. Probabilities are given a value between 0 (will not occur) and 1 (will occur).[1] The higher the probability of an event, the more certain we are that the event will occur. The concept has been given an axiomatic mathematical derivation in probability theory, which is used widely in such areas of study as mathematics, statistics, finance, gambling, science, artificial intelligence/machine learning and philosophy to, for example, draw inferences about the expected frequency of events. Probability theory is also used to describe the underlying mechanics and regularities of complex systems. answer: Therefore, the probability is .0008 as accurately calculated by moi, put another way: a SWAG. [still trolling for likes, please feel free to 'like' this. ]
But the two are not mutually exclusive. Build the collection and gain the reputation, then sell and have the money too. You might be surprised at how good museums have been getting at getting out of such restrictions and selling donations.
I imagine it may be easy for lesser donations. I have donated some items of importance to a museum before, but they are lower value so I imagine if they sold it in violation of my wishes I wouldn't know it. However, I believe it would be tougher for some more well known pieces.