Is the teacher to hold the student accountable for the full number of sessions agreed upon monthly, or for the actual sessions the student took, given that the teacher incurred financial losses and rejected other opportunities due to this agreement?

So long as the agreement between the two parties is for monthly work, consisting of eight sessions divided over known days for 1600 Riyals, then the employee is entitled to the full wage upon the expiration of the period and the beneficiary's enabling of their share, whether the beneficiary attends or apologizes. This is because a private employee is entitled to their wage by making themselves available for work for the hirer during the lease period.