Trello does the undo-approach. Instead of showing a loader after adding a member to a card, they immediately add it to the board, and then undo the action if an error occurs. In addition, they show a growl about the error.
My question is, is this UX fine for slow connections? Is misinformation the only big downside (that the user thought that the members were added successfully although they weren't yet) if for example they immediately closed down the application even before the request even made it? Are there any ways to mitigate or prevent that?