If we go ... / If you see ... / etc.

If (I'm / I'll be) late this evening, don't wait for me.

Will you call me if (I give / I'll give) you my phone number?

If there (is / will be) a fire, the alarm will ring.

If I don't see you tomorrow morning, (I call / I'll call) you in the evening.

(I'm / I'll be) surprised if Martin and Jane (get / will get) married.

(Do you go / Will you go) to the party if (they invite / they'll invite) you?