if...

would anyone explains what this sentence mean?
He mused on how different his life would have been, had he not met Louisa.

Is it true to rephrase it as:
He profoundly thought of how different his life would have been, if he hadn’t met Louisa.

is it grammatical role to omit if and change the if clause to question form?

Hi,

This inversion is just another way of expressing a ‘conditional’ idea in place of ‘if’ as in:

Had I known this would happen, I wouldn’t have gone.

This kind of construction is usually restricted to what is called an ‘impossible’ condition.

Alan