"Will I have to...?" asks if it will be required in the future at some point - not if you are expected to do it right now.
"Do I have to...?" is more flexible, it asks if it is required now - but can also be used of known requirements to do something in the future.
If unsure, prefer "do I have to".
Separately, "come there" can seem a little awkward. The rules of when it's better to use "come" or "go" are somewhat tricky. Any of "come along" (if you're both going to the meeting in the same direction) "come to you", "come to the meeting", or just "attend" might be better.
Also consider "Would you like me to..." or simply "Should I...?", as "have to" gives a faint impression you'd rather not be at the meeting unless absolutely necessary, whereas you may prefer to convey a willingness to come.
As you put it later "Am I required to be there?" is perfectly fine.
The sentence as it stands there is not correct.
This is due to the circumstance that to sleep is usually an intransitive verb that does not take an object. With the leading was the construction would be passive voice, but English doesn't use intransitive verbs that way. However, intransitive verbs can use the past continuous and thereby was sleeping.
sleep intransitive verb
to rest in a state of sleep - MW
Admittedly there are transitive uses of sleep, but they do not fit in the construction of the sentence in the question.
The problem with intransitive verbs is that they don't go over into a passive voice. I.e. you can't be slept. If it was a transitive verb that took an object that would easily be understood. Take the transitive verb to slap for example.
I was slapped when he came back to the home.
This sentence offers two explanations at once. Firstly it's homophone to the sentence from the original question. Thus, it might be what was spoken if the question is based on something heard.
Secondly it shows that two past tense verbs can actually be just simple past but in a passive construction.
In the most commonly considered type of passive clause, a form of the verb be (or sometimes get) is used as an auxiliary together with the past participle of a transitive verb; - Wiki: Passive Voice
A transitive verb is a verb that requires one or more objects. This contrasts with intransitive verbs, which do not have objects. Transitivity is traditionally thought of as a global property of a clause, by which activity is transferred from an agent to a patient. - Wiki: Transitive verbs
Best Answer
They're all correct, but they have different meanings.
"What if I come back for you" is an offer. "I am offering to come back for you, if ...".
"What if I came back for you" is weaker, a request for information. "Tell me what you would do if I came back for you, then I will decide". It's hypothetical.
I think in many cases the difference in meaning is subtle and not very important.