Technically, the C/D can be left in the hangar overnight with a stock of replacement parts, the tomtens will get to work and a shiny new E model will be there in the morning.
That was the original Swedish plan - although it was both economically frugal and politically feasible at the time, and it's mostly the Pootster who has changed the latter equation. On the operational side, the RSwAF decided that it did not want to go through a period where a lot of its jets were in the factory being rebuilt.
But in the next few years, with rolling E/F production between Sweden and Brazil, I would expect that there might not even be an economic case for building them by conversion.