Indeed, there is nothing wrong with the serial monitor, it will run for as long as the power is on. I can't see how there can be anything wrong with your code and, if you just use the standard IDE like everybody else does, you should be OK.
I might point out that, since you are formatting output into CSV, you are surely better off using RealTerm anyway, instead of the serial monitor. RealTerm is a proper terminal programme, not an alternative serial monitor. It enables you to record the data directly to a CSV file for further use at leisure.