I very much doubt that when employment comes it will entail flying a PA-34 et al
Had to laugh at that! Several of my friend's I trained with are flying Seneca's for their 1st job...!
Getting back to your Q - I'd recommend keeping everything current, as employers will prefer this when comparing CV's.
Unless you plan to renew your IR on an approved sim, or single-engined aircraft, you may as well renew your MEP in the same flight.
Does the status of your MEP Rating have any impact on your multi-IR
Yes, everything. The 'Multi' part of your Multi-IR refers to the Multi rating, so assuming your MEP has lapsed, you won't be legal to fly Multi Engined Piston aircraft, despite having a valid IR rating.
However, if you're talking flying multi-engined type rated aircraft (eg turboprop/fan etc), then your MEP rating has nothing to do with this and you can let it lapse.