No one can answer this question - because it depends on the strength of your application and its supporting documents. It also depends if this is the first time you are applying or if you have a previous history of Schengen travel.
However, I will note one point that your visa will not be canceled / invalidated if it is issued after the flight date. The flight reservation is used as proof that you intend to return to the country, and to validate your travel itinerary.
If you receive the visa after the 12th, it will still be valid.
I am not aware of any guidelines that specifically state priority of visa processing based on travel date - in fact, all the documentation that I have seen advises people to apply well in advance of their travel date to ensure that their application is processed in time; simply because there are too many variables that go into the application process and it is difficult to pin down a date.
Just some anecdotal evidence from my own experience applying for Schengen:
The first time I applied, it took 21 days and I received my passport 2 days before my flight. I applied approximately one month in advance of my travel, since I knew that this is the first time and it may take a while since I am not a known entity to the Schengen system. I received a visa which was valid for a single entry and only for the dates of my trip (it was a 14 day visa).
The second time around I applied 14 days before my travel date. My passport was returned on the 5th day and this time I was issued a multiple entry visa which was valid for 4 months.
At the same time, a colleague of mine applied for a visa for the same country and the same purpose of visit. His application took 30 days (first timer) and his visa was for 10 days.
The third person in our party got his passport back in 3 days and he was given a 5 year multiple entry visa (he had the most travel history).