I can sympathise with the sales department - I used to work there in a previous life - and it's not so fun to get requests from customers who don't want the new version or maintenance and just want something for free, especially when it's the customer who's lost their disk. Did your user register the software with Datawatch? Did you ever have maintenance in place? If you did have maintenance, you'd be entitled to the latest version for free. But if you've got several users about to upgrade, I would have thought that it would be possible as a buyer to talk to sales and ask them for an offer. Hopefully you'll be able to take out maintenance this time
Could I also point out that if the user has a new PC, that it might have versions of Windows, .NET and Office running which aren't necessarily compatible with Monarch v8, which dates back to the days of XP, Office 2003 and .NET 1.0 (I think). Upgrading will let you handle Office 2007 and 2010 formats, as well as more PDF options and XPS input, along with 64 bit support and quite a few helpful features (Column(), Cleared By, floating Field List, multiple Footers,...).