The carts will be around for a while. It keeps the Dubbies busy and they feel important and relevant.
They will get rid of the carts and door to door when it is just too embarrassing for the dubs to be in public. If JW's can not defend themselves, they get nervous.
Once it gets to that point, WT will tell the rank and file that the ark doors are closing and Jah's message has been given to all. The preaching work is complete. Fear, obligation and guilt work wonders! If it did not work, WT would not continue to use it!