I do not know where all this information comes from, but reading
Wikipedia, I understand that although Sieera stopped developing and doing business at different times, the ownership if its brand (and thus its intellectual properties) remained owned by Vivendi, which evetually merged with Activision.
Sierra earned some new ones in 2005 as a publisher when no development whatsoever was done there.
To my understanding, Activision has all the required cards in its hands to successfully reboot Sierra (again).
Now, does that mean anything for the old niche franchise SWAT is? I hope they will see the potential, knowing people still play the 4th opus.
However, all things considered, SWAT 4 is a niche: overall the fanbase is not really big. The studio could decide to use some more popular franchises to (quickly) make money.
The fact is there is no good tactical FPS except for our beloved SWAT 4. That could be an asset ruling in our favor.