Missing

A coworker who only comes in Mondays, Wednesdays, Fridays and Saturdays has not come in Monday or today. Should I be worried? Instincts says no, he is probably dealing with school issues. But I am wondering what he could be doing. He is the only one who routinely answers my pages, and I like knowing he is somewhere in the store in the event that I need him. Also, because he has not been coming in, my manager puts two people on the floor. Which would lead me to believe he has requested time off, because otherwise how would my manager know to schedule the two we need to replace him? So many questions, and none of it is my business.