Hi!
Okay, I think Serendipity 1.1.2 still can exhibit the behaviour to make trackbacks fail when xml-rpc pings fail completely. Some work to improve this has been done in the current 1.2 snapshots.
In cases where a pingback fails, resaving the article should work - if not, you can save the article as draft again, then publish it again (Without checking the 'Send xml-rpc pings' boxes) to perform it.
If you have the time, you might want to try out the recent snapshots and see if they help your problem?
As an addendum, I also discovered that if I take out the failing ping, and hit publish again, the article is actually published again and I now have two articles, one of which I have to delete.
Yes, if you hit "save" again with a aborted save progress, s9y was not able to update your entry form to tell it which entry id the recent entry has assigned (this is done via javascript after an entry is saved). So in your case you would first need to leave the form and edit the existing entry instead...
HTH,
Garvin