There were rumours that NAV will be joined with GP someday. Therefore, some people might be afraid of upgrading to new version of NAV, and think about moving to AXAPTA instead.
Any ideas, how to make these people believe that NAV will stay for quite a while?

Any facts?
Comments
If you have access to partnersource you can download the roadmaps produced by MS - they commit further into the future for the NAV product than many software authors do!
As for thinking about AX over NAV there needs to be a business and budget reason for the choice, choose the right solution for the business, they are not simply interchangeable products despite being both Dynamics products.
The rumor I heard is that MSFT GP will be joined with NAV since the sale of GP has been stagnant and sale of NAV has been skyrocketing. 8)
AP Commerce, Inc. = where I work
Getting Started with Dynamics NAV 2013 Application Development = my book
Implementing Microsoft Dynamics NAV - 3rd Edition = my 2nd book