British English has many phrases for a plan that is set aside without ever being ended.
To kick something into the long grass: To delay a matter in the hope that it will be forgotten.
To put something on the back burner: To set it aside for now, and often for good.
To quietly shelve: To abandon a plan without announcing it.
It’s gone quiet: The other side has stopped replying. The deal is probably dead.
It fell by the wayside: Nobody ended it. It simply stopped.
To take French leave: To leave without saying goodbye or asking permission.