I never even finished form 5 (11) but ended up driving planes having never gone any further with my education, today however is a diff story, the Airlines don't consider the ability to fly as their number one priority (they will find that out soon enough) it's the ability to bluff their psyche crap people & have a long list of degrees on yr CV, any mug can drive a plane, it's the hairy fairy stuff that's the difficult part!
In answer to your question.Yes finish year 12 as it's needed to get the job not to fly a plane!
Do what you have to do (bluff them) to get into that shiny jet, figure out the rest along the way:-)