* Chrome web store support page. It is a default option. The user can complain there if something doesn't work.
* Implement a complain button in the extension and if something broke and X users clicked the button, I will take action. IMHO It would be nice to have a central maintenance point which the extension will check and in case If you turned on 'maintenance mode' then just show a dialog to users like: The extension isn’t working properly right now. It will automatically be disabled. What to do? [Disable], [Keep it running]
* automatic way: try to build a heuristic system which will monitor changes in the layout and notify to the developer of any issues.
In any case, there will always be a time when the extension would not work if Twitter changes something globally.
I'll be very happy if this functionality will be implemented on the Twitter side.