Can I just add that I think you can keep your MEIR current without renewing your MEP?
You would obviously lose MEP privileges but so long as you keep renewing your MEIR in a MEP aircraft (or sim every other year) you can technically still keep your MEIR without letting it drop down to an SEIR - although I have no idea how hard it would be to pass the MEIR renewal if you're not flying MEP aircraft in between tests.