I would only be concerned if your child is in 1st grade. If so, I would monitor homework closely to make sure that your child does not fall through the cracks.
When my son was in 1st grade, on Meet the Teacher night the teacher announced that she was pregnant and planning to move back to her hometown (somewhere else in Texas) and quit teaching. It appeared she was there for the health insurance. It was a horrible year.
Because he was my first child, I didn't know how involved to be and the teacher didn't really communicate with me, so I didn't realize how far behind he had fallen. We had to do a lot of catch up over the summer to make up for her lack of communication and interest.
Just remember, "the squeaky wheel gets the grease." No one will advocate for your child; YOU have to do it. BUT, you don't have to do it in such a way that you burn bridges and make enemies with the principal (or future teachers). Do things like volunteer to help the current teacher, even if it's just cutting out laminating or copying worksheets. When the teacher goes on leave, be in the position of being the person she tells the substitute to call on for help. Then you will have the inside track and can know what's going on.
Oh and by the way, when my son's teacher left, we were so thankful. The teacher they hired to replace her was ten times better than the original teacher.
Hope this helps!
W. in Carrollton