No, you don't need to re-install FileManager. Even if your account is negative, you should still be able to open FileManager. DriveHQ offers 1 month grace period. So if your account balance becomes negative, your service should not be impacted within 1 month. After 1 month, you can still open FileManager. You can still upload files and manage files, but you cannot download any large files.
If you cannot open FileManager, probably it is already running? If so, you can click on the small FileManager icon in the System Notification area (bottom-right corner of your screen) to open it.