Absolutely. V1 will never 'expire', and the licenses you have for it are perpetual. You can upgrade if and when you like, and when you do, you'll receive all versions for 12 months after you buy the upgrade.

The only thing to remember is that NCrunch does need to be updated regularly to be kept working with new versions of test frameworks, Visual Studio, etc. If you're running on an old version, there may not be much I can do to help if NCrunch suddenly breaks in response to changes in your development environment. Of course, if this ever is a problem for you, you can just purchase the upgrade license and upgrade when you need to.