Re: "be supposed to" in "hypothetical context"
The only one of these that makes any sense with "supposed to" is the third and even then it's a stretch to say it's natural. The rest would be far more natural as:
Originally Posted by GentleBoy
The meeting is cancelled. I would have to stay back otherwise.
The meeting was cancelled. I would have had to stay back otherwise.
If the meeting was in the morning, he would have to arrive at 5 o'clock.
If the meeting was in the morning, he would have to come at 5 o'clock.
It's difficult to use "supposed to" with conditionals.
The meeting is in the morning so I'm supposed to come in at 5am!
If the meeting is in the morning, I'll have to come in at 5am.
About the only examples I can come up with are things like:
If I'm supposed to arrive at 5am, you'll have to pay for a taxi for me.
If he's supposed to be King Henry, why isn't he wearing a crown?
As you can see, the "supposed to" part is in the same part of the sentence as the conditional "If".
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.