If you want to MAKE SURE that you want the new data to be entered everytime,(in another way overwriting) You should drag a File System Task and put it on the very beginning of your package. In the Control flow before your data flow. Then select delete file content in it.

So, basically everytime you run this package, before anything happens, it will delete the content so that new datas are inserted. SO, you would not have to worry about whether it got overwritten or not. The data will be fresh for you each time.