As the Islamic State’s hold on territory was gradually diminished in Iraq and Syria, countries around the world expressed concern that the group’s large contingent of foreign terrorist fighters (FTFs) would return to their home countries to continue their campaign of violence. However, as time has passed and relatively few attacks have taken place, some wonder if the threat has passed. This article argues that an FTF returning directly to their country to commit an act of violence is only one way that such a threat may manifest itself, but that there are other ways that may ultimately take longer to appear. This article utilises the network of individuals responsible for carrying out the 11 September 2001 terrorist attacks as a case study to demonstrate the various pathways and timeframes through which FTFs may pose a future threat. This approach reveals that, although the concern of FTFs directly returning to participate in attacks is valid, the varied and long-term ways in which FTFs may ultimately pose a threat are of equal if not greater concern.