I have just noticed that the grommet at the rear end of the swing arm that the derailleur cable passes through has disappeared up inside the swing arm.

It must still be on the cable, but how do I get it back out? I am planning on changing the cable & outer soon, so will tackle it then, but if anyone has had this happen and solved the problem then I would love to know how you did it.

One thought I have had is to tie something on to the cable like a zip tie that will pass through the hole in the frame but not the hole in the grommet, and then pull the cable through hoping it will bring the grommet with it.