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) can be used to augment the User Interface, these features cannot be used as a substitute for physical button sequences that must be used to trigger system recovery actions. Sooner or later, as now, you will encounter a situation from which you cannot recover.
Until repaired, you will not be able to resolve a locked-out (disabled) iPad, reset a forgotten device passcode, or restore your iPad using DFU/recovery mode.
You can arrange repair of your iPad either by (a) visiting the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - or (b) using Apple's mail-in repair service:
Genius Bar Reservation and Apple Support Options - Apple
iPad Repair & Service - Apple Support