The first step is to check the warranty status of the Surface Pro 11 and see whether Microsoft Complete or any other accidental-damage coverage was purchased with the device. If accidental-damage coverage is active, the repair/replacement may be handled under that plan, subject to its terms and any applicable service fee.
If there is no accidental-damage coverage, Microsoft Support can confirm whether the device is eligible for an out-of-warranty service replacement and provide the applicable cost. Microsoft generally does not treat the lack of a protective case as a reason to cover accidental damage under the standard warranty.
I would recommend contacting Microsoft Surface Support with the device's serial number. They can confirm the exact warranty status and available service options for your particular device and region.
Unfortunately, there is usually no standard warranty exception simply because the Surface Pro 11 does not have an official bumper or protective case.