I know the perfect way to wrap up this franchise .
If skynet can't be stopped then they need to reprogram skynet before it goes online.
In the final movie they find some piece of code or module that makes sky net capable of killing people indiscriminately and seek to replace it with something that helps humanity. Sky net gets to a point it can connect the dots on virtually all crime from the lowest to the secret elite of the world and expose all threats to humanity.
In the final scene they replace the code or module and think they prevented sky net from launching.
Instead of n0000ks tactical missiles are launched at millions of targets that have been identified as hostile based on their footprints in the world compiled by sky nets quantum computing of digital, video audio, and satellite feeds. There is destruction but not to the degree of world cataclysm
Millions of degenerates are crushed at once leaving only the "good" people to start over with the help of sky net which is now programmed to live to protect humanity instead of itself