The differences you mention correspond to the following definitions:
Expect verb
1 Regard (something) as likely to happen.
1.4 Require (someone) to fulfil an obligation.
[with object and infinitive] ‘we expect employers to pay a reasonable salary’
- ODO
When an expectation is made of a person, it tends to be taken as a demand. When it is made regarding an event, it tends to be taken as an expression of likelihood.
Consider the following examples:
- A: I expect you to pass this exam. B: Yes, Sir!
- A: I expect that you will pass this exam. B: Thank you!
These follow the pattern described above: expect [person] implies a demand; expect [event] implies likelihood.
However, consider changing the second example's response to that of the first:
- A: I expect that you will pass this exam. B: Yes, Sir!
The sentence that was treated as an expression of likelihood is now treated as a demand.
The attitude of the speaker, their general demeanour, and the context in general must all be taken into account. As (2) and (3) demonstrate, there is no simple test for disambiguation that works in all situations. However, the earlier comment regarding the difference between (1) and (2) provides a useful rule of thumb.
You ask about disambiguating the following, which I will number for convenience:
- I expect not to hear from you again.
Consider the following similar sentences, coloured with a little context:
- I was looking for you for so long. I expected not to hear from you again.
- Explain yourself! I expected not to hear from you again.
- He was poorly treated. I expect not to hear from him again. You should apologise anyway.
- Tell him I was poorly treated. I expect not to hear from him again.
- Tell him I was poorly treated, though I expect not to hear from him again.
The only difference in the sentence between (4) and (5) is the tense of expect. However, the context of (5) makes clear that the expectation was an expression of likelihood, not a demand. In (6), keeping the sentence from (5) but changing the context gives a different sense - that of a past demand, perhaps from a headmaster to a recalcitrant trouble-maker.
Between (4) and (7), the difference is you vs him, just a switch in pronouns. The context of (7) contains no hint of a demand (of him). It's purely situational. Changing just the context to that of (8) colours the sentence as part of a sequence of demands. However, if we replace the first full stop with though (9), the sense is reversed and it's no longer a demand.
We now return to (4). By idiomatic usage (though probably more BrE than AmE), the context this suggests is closest to that of (8); it's read as a demand. To read it otherwise would require something explicit in the context, but even the following sits awkwardly as purely an expression of likelihood:
- She saw him board the boat headed for uncharted waters and whispered sadly, "So this is our final goodbye. I expect not to hear from you again."