External Drive Repair via Terminal...might erase disk0s1, Y or N?

If something goes wrong when attempting to repair the partition table it can cause you to lose access to the data. After all the partition table/map holds the basic layout information pointing to the actual partitions on the drive.

You should always have frequent and regular backups of your computer and any external media that contains important and unique data. Hardware can fail and file systems can become corrupted, plus data can be accidentally deleted.

If you are not able take the risk your data, then try using a data recovery app such as Data Rescue to try to recover your data instead assuming the hard drive is physically healthy. Or contact a professional data recovery service. If the drive is failing, then you want to minimize using the drive since it may make a physical drive failure worse. If the drive has a physical failure, then you may only have one chance to recover the data from this drive so choose wisely.

You can try to check the health of the external drive by using DriveDx. You will need to install a special USB driver in order for DriveDx to attempt to access the health information on the external drive. However, even with this special driver some external drives will block the necessary communication. If there are any "Failing" or "Warning" notices for the hard drive it means the drive has a physical failure or it is worn out respectively. This doesn't always apply to SSDs.

Without knowing whether the hard drive is healthy I cannot say if it is a good idea. If the hard drive is healthy and you are comfortable with the possible risk, then go ahead. It is possible that the partition table issue will need to be addressed before any data recovery software will be able to access the data on the drive. Personally I always attempt to check the health of the hard drive just so I know that I'm not making a physical drive failure worse.

Even if the external drive is physically healthy it can be wise to make a low level bit for bit clone of the drive to another drive of equal or larger size and attempt to repair the clone so you leave the original drive untouched in case you make a mistake or decide you need a professional data recovery service. However, the only utility I know which is reliable on making a bit for bit clone is a command line utility "GNU ddrescue", but it is easy to make a mistake and overwrite the wrong drive and destroy the data you are trying to recover.

This type of issue can be very complex especially if there are no backups of the data as we are missing a lot of critical information especially since we cannot actually see the drive ourselves. If the hard drive has a physical failure, then no I would not attempt any repairs on the failing drive. If the hard drive is healthy, then it can be worth the risk to attempt to repair the partition table, but only you can decide if it is worth the risk as it is your data.