What happens if a warrant officer fails to complete their skill producing course?

First off, get that failing mindset of out of your vocabulary. If you are thinking about failing, then you probably will fail. Warrant Officers regardless of MOS don't know how to fail. Secondly, you have to complete WOCS first, but if you fail the APFT twice or an exam twice you could be recycled or separated. If you make it through WOCS but fail out of flight school, you may have the oppurtunity to reclass at the needs of the Army Warrant Officer Cohort. Now keep in mind, I graduated WOCS and WOBC in 2007, so don't take my word as the gospel. The Army is downsizing, you could be separated at any moment so don't be suprised. I know many great Warrant Officers who got passed over for promotion to CW3/4/5 and had to separate or retire if they had enough time to retire. So separating a WOCS candidate or a newly minted WO1 would not be difficult. I would recommend contacting the United States Army Warrant Officer Recruitors if you have any questions like that.

http://www.usarec.army.mil/hq/warrant/

SGM Matthew Quick and @COL Charles Williams also gave you great advice. Good luck.

Why are you going into this with that failing mindset?

SPC (Join to see) You need some WOs to chime in... I believe you go to Warrant Officer Candidate School First, them Flight School. If you are already a Warrant Officer, and fail to complete that course, I suspect you would go to another career field based on the needs of the Army. But, you need to adopt "failure is not an option." If you are physically and mentality qualified to be selected and attend, you are capable of completing the journey if you want it bad enough.

http://www.goarmy.com/careers-and-jobs/current-and-prior-service/advance-your-career/warrant-officer/flight-warrant-officers.html