Oregon Revised Statutes Education and Culture § 342.545

(1) Sickness or other unavoidable circumstances which prevent the teacher from teaching 20 school days immediately following exhaustion of sick leave accumulated under ORS 332.507 shall be sufficient reason for the school board to place the teacher on leave without pay for the remainder of the regular school year and to terminate the teacher's employment without penalty on August 1 if the school board determines that the teacher is unable to resume teaching responsibilities at the beginning of the next fall term. This subsection applies to teachers whose employment is based either upon contract or tenure, or both.

(2) A district school board may release a teacher from a contract by mutual agreement. No board is required to consider any resignation not in writing.