All DVD Burner manufactures provide the MTBF (Mean Time Before Failure) expressed in POH (Power On Hours) of their products.
You need to refer to the particular LightScribe DVD Burner manufacturer and review the particular LightScribe Drive Specification where the MTBF (Mean Time Before Failure) is provided for the particular Drive.
A short PCWorld article concerning DVD Burner Life Span ->
Your logic appears to be flawed. It doesn’t make much sense paying the extra expense for a LightScribe DVD Burner if in an effort to extend the DVD Burner lifetime you don’t intend to use the LightScribe function. It would be cheaper to purchase a non-LightScribe DVD Burner if you don’t have intention of burning LightScribe Labels.