Do I have to complete all my assignments before the strike?

No. The course syllabus you received (in September or January most likely) works like a “contract.” This means that your professor cannot ask you to complete work earlier than the dates set out in that syllabus.  If job action is taken assignments will be due at a later date, proportionate to the length of the strike and in accordance with the remediation plan determined by Senate (York University’s governing body)