There have been no further messages : is it safe therefore to assume there was no harm done ?
It is always recommended to unmount removable drives before disconnecting. This even includes camera cards. That being said, if the drive appears to working as expected, it's probably fine.
- these items are all plugged in to a surge protector strip. Is it also OK to disconnect plugs while the strip is switched on ?
If the exteranl drive is off, it's fine to uplug it if from the strip, if the strip is still on.