I am going to offer a simpler explanation making reference to the previous answers and comments (avoiding any consideration of changing は or が ) :
Both are acceptable, both indicate the actor is not expected to visit but there is a difference which can be shown by the following which are quite close to the normal translation of はず into standard English:
彼は来ないはずです。| I expect he won't come.
彼は来るはずがない。| I have no expectation of him coming [at all].
As explained by 明鏡国語辞典 (in Snailplane's comment), the second case is much stronger because the speaker is excluding any possiblity of the actor coming. (皆無＝＞"There is no chance he is coming.")
This was not part of the question but it is a worthwhile comparison:
はずがない and わけがない are taught as interchangeable. I rationalise this on the basis that わけ is used to convey circumstances or a reason, as follows:
He has no reason to come.
He is not coming under any circumstances.
(~There are no circumstances under which he will come.)
=> I have no expectation of him coming [at all].
The expression 「彼は来ないわけです。」, on the other hand, might be used to explain: "That is because he is not coming.", or depending on the situation: "Yes but he is not coming."