I’d have thought a restaurant has to have safety glass – toughened or laminated fitted in case a customer falls against the window.
Given the circumstances you are morally liable for the damage to the window but I’d be asking the question why it clearly wasn’t safety glass.
I’d be inclined to point out the 1992 Health, Safety and Welfare Regulation 14 requiring that “every window or other transparent or translucent surface in a wall, partition, door or gate should, where necessary for reasons of health or safety, be of a safety material or be protected against breakage of the transparent or translucent material; and be appropriately marked or incorporate features to make it apparent.” This regulation applies to a wide range of workplaces including offices, shops, schools, hospitals, hotels and places of entertainment. Despite this, reported incidents of glass breakage are on the rise.
I suspect you’ll not hear any more from them unless you decide to pursue a claim yourself.