A new license does NOT need to be purchased as part of the upgrade (assuming your service contract is still up to date and has not expired).
The license is not tied to a specific IPS version, and is instead tied to a support contract for the hardware. That support contract covers all IPS versions that support that particular hardware.
During normal "upgrades" the existing license will be carried forward during thr upgrade in a similar way that the existing configuration is carried forward from the older version to the newer version.
Some users will choose to not go through the normal "upgrade" process and instead choose to use a "System Re-Imaging" process to get to the new version.
NOTE: In the case of the SSM-20, the "System Re-Image" process uses the "hw-module module 1 recover" commands of the ASA. This is not a normal "upgrade" process and winds up erasing both the configuration of the sensor and the current license.
However, even if a "System Re-Image" process is used; it does NOT require a new "purchase" of a license.
The license may be deleted off the sensor, but you can still go back to cisco.com and request another copy of your current license.
It will take some additional steps to get the license, but is NOT additional cost.
So the only time you need to "purchase" a license is if your existing service contract has expired. And regardless of which IPS version you are running, you will need to purchase a renewal of your service contract.
