Performing a system software update carries an element of risk - in that should the update process fail, you may be left with a "bricked" device. While unrecoverable issues are rare, they can and do occur - very often due to either the update process being interrupted by the User, or sometimes due to a hardware failure.
Issues of this nature will be resolved by Apple while your device remains in warranty - or if you have an active AppleCare+ plan. If your iPad suffers a failure outside of its warranty period, howsoever caused, the problem will be addressed as a chargeable repair.
You can check availability/eligibility for repair - and associated cost for your country/region - here:
iPad Repair & Service - Apple Support
In addition to Apple's mail-in repair service, you can arrange repair at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP):
Genius Bar Reservation and Apple Support Options - Apple
For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair while expensive will be somewhat less than the cost of a replacement iPad.
If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.