I think it's very common to have an imperative in the second half (apodosis) of a conditional sentence.
ει υιος ει του θεου, ειπε ινα οι λιθοι ουτιο αρτοι γενωνται. Greek New Testament, Matthew 4:3.
If you are the son of god, tell these stones to be bread.
In your 2nd example, I think the "I'm afraid" would normally be "I will be afraid." In that case, the future indicative would work just fine in Greek.
In your 3rd example, you could use an imperative. δει σε καλεῖν... would work, too.
What does NOT work, I'm pretty sure, is to put that second half into subjunctive. I'd like to hear from someone on that. You wouldn't say the following, would you?
εἰ συ αρξεις ἀποπτύειν, συ καλέσῃς τὸν ἰατρόν.
if you start to vomit, you call (subj aor) the doctor.
This is a point I get confused on because a 2nd language I know (a Bantu one) has a subjunctive that is Greek-like in many ways, but I think in this it is different. In Greek we can only have hortatory in the first person or a sort of "ου μη hortatory" in the 2nd or 3rd person. But you cannot just say καλέσῃς and mean "you should call," can you?
I will babble until I talk. ετι λαλαγω...