大家RA的通知书里有没有对RA取消的规定

我收到一个大学的RA，他说Your assistantship is dependent upon satisfactory performance in all department requirements, including placement exams. If your assistantship is withdrawn for unsatisfactory performance, you will be responsible for all tuition and living expenses. 我问一下大家收到的offer 有没有类似的限制？ 比如说一年的offer，他几个月后还能给我要回去？