I doubt Germany plus Italy and he Netherlands lack the technical capacity to build a plane on their own and certainly given the projects they were running (AVS, VJ101, VAK191, Fiat G95) the governments in question didn't really think so. Still if it fails to work out the logical candidate is probably not F/A-18 but Northrop's F-18L. Regarding 1 or 2 engines the NKF design was certainly single engined. I suppose its possible that you go to something like Panavia 100 instead but wouldn't take it for granted. Having Marcel Dassault happy with the project is I suspect the key component... but the proper POD here is SNECMA in 1959 teaming up with Bristol instead of P&W. Instead of TF306 they are building an engine that start from the core of the Pegasus together with Bristol which is what ends up powering ACF/AFVG... and the Mirage F3/F3M that goes to complement it.