Probably not the best planning to try to cram it into 1 day just before it is due to expire but you might have circumstances that have stopped you getting it done earlier, if your IR does expire you will have to do it in the aircraft this year rather than the sim.
Depending where you go you might have a sim set up as a DA42 with simulated glass cockpit and central control column or it may be set up as a generic MEP with traditional control yoke and simulated analogue instruments.
How tough the examiner will be depends upon the individual, you should expect to fly a full IR skills test profile with ILS and NDB approaches (one approach will be single engine) with an engine failure during the climb out from the twin engine approach. Both approaches will be down to MDA/ DH followed by a go around and then into twin engine GH. The final approach will be single engine go around into single engine circuit to land.
My experience has been that the revalidation test is way more relaxed than the initial skills test and examiners have been more than happy to reset and redo an exercise if it hasn’t gone well so I wouldn’t stress too much if I were you.
You will be required to simulate ATC calls and the examiner will play the role of the controller.
Good luck.