I think it's pretty clear that the 3000T series is the replacement for the 3000A. If I recall correctly, at one point the A and T even had the same price for the same combinations of channels, MSO option, and bandwidth. Looking at it now, the T series is slightly cheaper and also has more decode and other licensable options.
The 3000A series can still be found by searching for it, but it does not appear on the main scope web page. Amongst others, it now shows the 3000T along with the 2000A series
I'm not sure why they're continuing to sell the 3000A series. It hasn't had any significant new features added to it for years and only a minor bug fix here and there.
To a certain extent, possibly. There are digital certificates there that have expiry.
I can only speak for the 3000A because I have one: The purchased licenses do not expire.