The EASA proposal on the EIR states that SIDs and STARs will not be permitted on the EIR, which means the pilot will have to cancel IFR at the end of his enroute segment.
Now.... he will obviously be aware of that
so he will file a route whose terminating waypoint is
not the first waypoint of a STAR (which is what you do in "classical" IFR) but will be somewhere "handy" for a DIY descent to the airport.
So that should deal with the lateral issue but it does not deal with the vertical issue if ATC forces you to cancel IFR before descending through altitude XXXX.
My experience is that one cannot remain on an IFR clearance below a certain level/altitude. I don't know what sets that level; it could be radar visibility. On a recent flight down the Adriatic I had to cancel IFR c. 3000ft to go any lower. I have little experience of this however because if you have an IR the absolutely very last thing you want to do is cancel IFR because ATC will generally wash their hands of you ("remain outside controlled airspace") when you do that, so you can fly into a trap whereby you need to sit and beg for a new IFR clearance to climb back up again, and that's a dangerous situation to be in
Maybe some European ATCOs can input here re the lowest levels available for IFR. Is it the MVA, perhaps?