Last year
Last year there was an option if you fail WizzAir interview to go to SmartLynx, however they changed it this year. Basically if you pass the BA assessment, your results will be presented to both Airlines. Based on your overall results (compass, profile xt and BA interview) one of the companies will pick you for further interviews. If for some reason you fail on this interview, you do not have chance to try for the other company. This is information I got from BA managers.