Motor Uncashed cheque never honoured?

My wife was involved in a car accident in 2006, which the other party agreed to pay for without admitting liability. Both insurance companies were involved. We got the 600 euro cheque but forgot to cash it and the cheque became uncashable after 6 months. I wrote to the other party and asked for another cheque; they agreed that they would pay (in writing - I still have the letter) but said they couldn't send it at that point. It has never been received. I have chased on several occasions to different addresses.

I know where the person works now and can send a letter there; do I stand a chance of getting paid ... or has the intervening time between 2006 and 2011 mean they are off the hook?