Last week I went to the dealer for a timing belt change on my 97 N/A 5sp with 140k on the odometer. I specifically asked for the timing belt and tensioner to be replaced as many seem to recommend the tensioner be replaced every other tbelt change. When I returned to pick up the car, the invoice came out lower than expected (a big surprise). When I asked the service advisor why the invoice was cheaper, he said that it had a hydraulic tensioner that didn't need to be replaced. Given that some have mentioned the possibility of the tensioner going bad and subsequently taking out their engines, should I be concerned? Should I go back to the dealer and ask them to replace the tensioner as agreed?
They did state on the invoice that no tensioner was needed at the time of the repair, so would this cover me in case it did fail?

Thanks in advance for your advice.