Hi,
TestComplete licenses are perpetual and you can use them as long as the licensed version of TestComplete supports technologies of your tested application.
With initial license purchase you are getting subscription for one year and you are eligible to get major and minor TestComplete upgrades within this period of time. After your subscription expires, you need either to extend it or to stick to your latest available version of TestComplete.
For detailed information about subscription extension pricing contact either your SmartBear Sales Representative directly or via the https://support.smartbear.com/message/?prod=TestComplete form.