How do you react when your direct Department Line Manager tells you to resign,treats you so bad and underscores your annual appraisal and pay rise?

I will request for the reason for such an instruction. If the reason is ethical, I will comply but if the reason is unprofessional and unethical, Management should be alerted.

Will speak to him with cool mind and try to convince him. Getting angry wont solve any problem.

I will keep calm but will not resign but request for my appraisal to be reviewed by his own manager since my performance in my daily task and other challenges is there to speak for me.

No panic, i will ask him that why do i need to resign. If the reason of my poor performance, why was i informed about it.

So easy issue, because there will be a succession plan will be established from the beginning to be ready for these kinds of surprises. This means the main duties and task of any person to be delegated to others as per there skills and roles, in other words, we have to plan from the beginning that each job to be handled by two person minimum and never we keep all eggs into one basket.