It is a common misconception that an iPad (or iPhone) can remain fully functional with damaged or defective physical buttons.
Whilst Accessibility features (such as assistive touch) and the Control Centre can be used as alternative access for some functions, these features cannot be used as a substitute for physical button sequences that must be used to trigger system recovery actions. If the physical buttons on your device are unresponsive or unreliable, sooner or later you will encounter a situation from which you cannot recover.
By example, if any of the physical volume or top buttons are not working, you will not be able to perform a forced-restart or resolve a locked-out (disabled) iPad.
Before the situation deteriorates further, you would be well advised to have your iPad repaired.
For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange a qualifying 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. This also has additional benefit in that the exchange iPad will have a new battery.
As for out-of-warranty repair costs, Apple offers a fixed-price price service, the cost of which will be determined by the type of fault. You can verify eligibility and cost for your region/country here:
iPad Repair & Service - Apple Support
If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee. If you don't have an AppleCare+ plan, you may wish to balance the potential repair cost against the option of replacing the iPad with a much newer model. Replacement with a newer model may be more expensive, but will offer benefits of a longer service life and improved capability and performance.
You might instead visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad - and you can explore your available options:
Genius Bar Reservation and Apple Support Options - Apple
