Can I use the -s and -ing form interchangeably if I'm talking about something in the future?
Person A:
Do you know when David gets his car back from the dealership?
Do you know when David is getting his car back from the dealership?
Person B:
He gets it back tomorrow.
He is getting it back tomorrow.
Person A:
Do you think Blaire can get pregnant again?
Person B:
I don't think there is a chance Blair ever gets pregnant again.
I don't think there is a chance of Blair getting pregnant again.
These sentences are actually all in present tense: we often use present tense to express future events.
We can present continuous form getting to talk about things that we are expecting to happen in the future, even if we are not sure exactly when they will happen.
We can also use present simple to talk about future event, but usually we only do this when we are talking about things that are scheduled or timetabled:
David's plane arrives at 07:45
The concert starts at 7pm.
Looking at your first example, about the car, present continuous is better because David getting his car back is not a timetabled event, however you will also hear people using present simple for this kind of dialog.
The second example is somewhat confusing because you use the word can which means is able to. Assuming that's what you meant, here is the question and answer.
Do you think that Blaire can get pregnant again?
No, I don't think that she can.
If you wanted to ask whether it is likely that Blaire will get pregnant again, I think that the future simple is better:
Do you think that Blaire will get pregnant again?
I don't think that there is a chance that Blair will ever get pregnant again.
