Hi!
Sorry to hear you’ve hit difficulties.
The TribeWooTickets class is still a part of the WooCommerce Tickets plugin – so long as it is indeed active you shouldn’t have any problems. However, if for any reason the custom code in your template runs and WooCommerce Tickets is not active, then you could indeed see this sort of problem.
One workaround is to test for the presence of the TribeWooTickets class before running those pieces of code, something like this:
if ( class_exists( 'TribeWooTickets' ) ) {
/* Add your remove/add action calls in here */
}
That should effectively insulate them from changes in the outside environment (such as WooCommerce Tickets being deactivated).
Does that help at all?