If a DVD Video object file (.vob) was burned on DVD which was ended up with having one or two bad sectors, would you be able to copy that file from DVD? I heard video files can still be played even if their data is in bad state but the header should be present. when you try to copy it, would you be able to get the same data or none at all?
One or two bad sectors in the file will not appreciably degrade the file, assuming you can get it off the DVD in the first place.
Due to the way that the video encoding/decoding process works I would expect there to be (at worst) a second or two where the picture looks "odd" after the bad data but after that the video should recover and continue to play.
As you stated the key data is the header, so long as this data is intact (along with the majority of the file) then the file should be playable.
The software DVD Decrypter is able to ignore errors and carry on copying data from a disc, but its use is of dubious legality. If this is your own personally made DVD then you should be fine.
Most standard utilites like Windows Explorer will halt at the first error and abort the copy. If the sector is truly bad you can't recover any data from it. So you can't get any data out of it. Assuming you can substitute the bad sector with all zeroes, it will likely still play in a standard DVD player but it might skip or degrade the quality of the video at that point.
I've used the free DVD Fab Decrypter just to copy scratched DVD's (these are non-commercial unencrypted home video DVDs) and it has worked for me in the past to salvage what is possible.