The Mirage 2000N's mission is likely a one way ticket, the Mirage 4000 in the same role purchases one farther from home. The 4000 could probably do a much better job than the D since it can carry more, farther without taking a hit to its thrust to weight. This would primarily relagate Mirage 2000 as a medium range interceptor in Armée de l'Air service and it would have to share its to air to ground avionics with the 4000 and 2000N for export orders. This could work somewhat similarly to the F-15/16 hi-lo mix in the USAF.
Export wise I don't see the Mirage 4000 making a big export splash at first, the aircraft would be too expensive for Australia, Canada, or the UK to buy. The only country that could afford them would be Saudi Arabia, who would buy an interceptor variant in the 1980s, followed by an air to ground model in the 1990s. Which in turn, would destabilize the F-15 production line back in the US. The Mirage 2000 would mostly retain most of its exports (Greece, Taiwan, UAE, Peru, India, Egypt, Brazil) since its capable air-to-air machine for its price and doesn't have political strings from the US or USSR attatched to it.
Buying the 4000 is probably going to hurt the Rafale's chances of surviving since further evolution (TVC, AESA, new engines, EO/IR sensors) of the 4000 could have given it parity air-to-air and air-to-ground wise with the latest Flanker and Eagle models for a much smaller cost to the taxpayer than developing the Rafale. There would have been a tug of war between the needs of the AdA, Aéronavale, Dassault and the bean counters. In the post cold war funding era it is likely that it would be the Rafale that would up the pretty technology demonstrator, while the Mirage 4000 would have been the one slugging it out with the Eurofighters, Grippens, Block 52+ F-16s, F-15Ks, F-18E/Fs, Su-30s and MiG-35s of the world for export orders.
Dassault would be in a perilous situation, in a desperate bid to save their baby they might team with a US contractor to get the Rafale built. Vought and Dassault had close ties throughout the 1960s and 1970s, and Vought had done an good job transitioning to from a primary to a secondary contractor in the 1980s without losing its independence. While this does seem unlikely, desperate times call for desperate measures. There was a massive hole left in US naval aviation by the cancellation of the A-12 Avenger II and the Rafale being the newest entry to the competition to replace the A-6E might have stirred some interest. Granted, it doesn't have much of a shot since McDonnell Douglas and Grumman would have raised bloody hell but it would have drawn more attention to the selection of the A-6 replacement and could have repercussions for the Super Hornet and Tomcat. Ultimately, the Aéronavale would have to purchase a Hornet variant to fly off the Clemenceau class/Charles De Gaulle in a massive dent to French pride. Though this is not without irony as the French had laughed Northrop back across the pond when they tried to sell the YF-17 to them. This would push Dassault into the UCAV field earlier and nEUROn might materialize sooner.
If the 4000 had gone into production I think it would have matured nicely with the backing of the AdA and could have gotten orders that the Rafale had lost; primarily, Singapore and South Korea where lacking radar and weapons integration hurt the Rafale. Brazil might also take a shining to it but budget wise a big order couldn't be placed. An evolved Mirage 4000 would also have an excellent chance in the 126 plane MMRCA competition in India or possibly even supplanted the Su-30 MKI.