It is a common misconception that an iPad (or iPhone) can remain fully functional with damaged or defective physical buttons. Intermittent function of physical buttons is symptomatic of contact failure - often due to dirt or moisture contamination
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 may encounter a situation from which you cannot recover.
Until repaired, you will not be able to resolve many issues - such as a locked-out (disabled) iPad, reset a forgotten device passcode or force-restart your iPad.
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