I think the fourgonette was replaced by the Express, in 1985. The Kangoo replaced the express.
I remember reading some French research paper about the process of designing the Twingo, which was designed as the R4 replacement. It said that there had been several projects since the seventies (as early as 1973) to replace the R4, but none had actually produced a replacement for various reasons.
I would love to get my hands on some of the designs for the replacement. I'm sure there were clay models, drawings, pictures of prototypes etc. I am sure they would be interesting from an R4 enthusiast's point of view as the designs would have resembled the R4 as late as the mid-eighties.
I wrote about it in my R4 history page:
http://www.geocities.com/richardirl/dando.html.... if the page happens to be available
And there is a picture of a Twingo design proposal on my New R4 section, that seems to have some R4esque features, unless it's my imagination.
http://www.geocities.com/richardirl/newrenault44.htm
Has anybody had a look at the development histories of the BMC/leyland/austin-rover site? It's an excellent site:
http://www.austin-rover.co.uk They have so many original pictures of prototypes and clay-models and design proposals.
I would love if somebody could properly document the history for the R4 in such a detailed way - including these design proposals, assuming they did in fact owe anything to the R4