All right, just to be technically correct: you don't need a current multi IR to start a multi crew type rating since the type rating will include a multi pilot IR - the original single pilot IR being of irrelevance other than to prove a point!
However, no company is likely to hire you without a current IR since it serves to demonstrate recent ability.
You can renew your multi IR in a sim - but not the multi rating. I suppose you can also renew both in a twin aircraft at short notice, too, so you could save your money and wait for a positive emplyment lead.
Having said that, if you leave it too long then you risk spending more money getting up to scratch. If the positive lead amounts to nothing you will at least have your rating for another year. So it begs the question: why not just keep it current?
It's a tough one, hope some information here helps with the decision.