what's the correct tense here: Is it "the past tense" or "the present tense"? "What if I miss the bus?" "What if I were late to dinner?" "What if I called her tomorrow?" "What if I don't understand?"
You may use either tense depending on the context or on what you want to convey.
You can even use will:
what if you will go
meaning what if you are willing to go.
Note that I didn’t use “I”: “what if I will go” which is grammatically correct, but illogical, or at least odd since I’m questioning myself if I’m willing to go.