Northern Delay Repay Ticket

I have an undated return ticket to anywhere on Northern network. Whilst I don't think it would be a good idea to try and use it at the present time, is it still valid and if so will it ever expire?

Recently discussed here: https://www.railforums.co.uk/thread...-their-validity-with-the-new-operator.197731/

Final post says yes. Personally I'd try to get it used in the next 1-2 years.