I'm not sure I have a definitive grammatical answer, but in my experience as a native American English speaker, the "didn't" variant is more correct and natural. Saying
I haven't heard from him.
implies that although you have not heard from him yet, there is some expectation you might hear from him in the future.
Whereas
I didn't hear from him.
is strictly talking about what is in the past. By using
I didn't hear from him until now.
you are adding contrast between the past and the present.
I suppose "I haven't heard from him until now" might be ok, but it seems like the "until now" (aha, something has changed!) conflicts with the hopefulness/tentativeness of "I haven't heard from him" — how can you still be hopeful if you already know that the situation has changed?
re: "until now" vs. "till now" vs. "up to now":
"till" is an informal variant of "until". (although The Free Dictionary says that till came before until historically) If you say "up to now", people will understand you, and I don't think it is grammatically incorrect, but it is somewhat unnatural-sounding. I think the reason is that "until" is such a common preposition and has a very good match for this situation, that alternative forms don't seem right.
Hope this helps!
Do you happen to know if she has a boyfriend? (I think there's a mistake, it should be if instead of is).
Happen +to infinitive means chance to do something or come about.
Happen to know means do you know by chance?..
Best Answer
In this sentence "just fine" means the same as "ok." It is slightly less positive than "well." It can also indicate that the person speaking is feeling defensive in response to the question.