The Law of Excluded Miracle in the language of guarded commands
The answer I can provide is I was reusing the definition of weakest precondition from the IMP language, but in fact I need a stronger definition. This definition looks as follows:

definition "wp c Q s ≡ (∃t. (c,s) ⇒ t) ∧ (∀ t'. (c,s) ⇒ t' ⟶ Q t')"


It is taking care of non-determinism. When one evaluates:

lemma excluded_miracle: "wp c (λ t. False) = (λ s. False)" 


One realizes that the statement is simply saying that the program either terminates, or does not terminate. Therefore, the import point now is to see whether my proposed definition is correct or can be improved in any way.