As with any job, if you do not perform to the desired expectations, it is possible that you may be released without pay. However, such a scenario is highly unlikely, especially if you were on an Exposure Tour and the team was able to watch you play prior to the signing of your contract. Most teams do not release players until the completion of the first half of the season in December, but again it is not likely to happen if you are trying hard and performing to the best of your capabilities.
It is also important to understand that in Europe your role as a professional foreign player extends beyond the court. Endearing yourself to the team, the sponsors and community fan base will improve your chances of retaining your contract and getting future contract offers.