The sentence indicated in subject should be correct.
If yes, why there is not inversion verb-subject?
What is the function of "What if"

Thanks!!!

Start with this sentence:

"If the key is lost, (then) a locksmith can cut another for you."

As you see, this is a usual \'if…then\' sentence.

As a question, it becomes:
"If the key is lost, (then) what should I do?"

Inverted, the sentence becomes:
"What should I do if the key is lost?\"
Here, you notice the expected verb-subject inversion: 'should I'

Then, shortening the sentence:
"What... if the key is lost?"
Now, it seems as if this question is not following the rules! ; but this is because we have omitted part of the sentence. The whole point of asking the question is to find out what I should do! It is not necessary to include the words, since the meaning remains clear. In the full sentence, the rule WAS obeyed, with the subject and verb inverted.

AFTERTHOUGHT:

The 'what if' construction is also useful when we don't expect an answer!

"I told you NOT to go near the edge! What if you had slipped? You would've fallen down the cliff!"

"What if there are sharks in the water? You won't want to swim in the sea then!"

Thanks for your clear explanation!!!
It's very interesting...

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