Yup, seems you guys were right. Removing a drive from the array trashes the entire volume, even the data that is still on the left-over drives still in the server is not accesible anymore. I was hoping that it would act like DrivePool under Windows Server 2012, where you can still access the data on the drives still left in the array, but it seems not. Yup, JBOD on Synology seems like a bad ideea, so i bought another 2TB drive, saved as much data as i could on it and on another external drive, deleted the volume, and created a SHR array with 1 parity drive, for peace of mind.
Thanks a lot