I see your point but it's not the first time the franchise did something of this magnitude. T3 killed Sarah off screen, TSCC implied she'll be dead soon and Genysis even went as far as erasing T1 and T2 out of its' new continuity (which I think is the worst offender in the history of the franchise). The franchise is pretty much a comic book multiverse right now with literally 5(!) separate contradicting stories that takes place after T2 with each of them claiming to be a sequel to it so I guess I went in the theaters with tempered expectations as long as they made good on the promise of Linda Hamilton kicking ass again, which she does.
Besides, we all know there will be another Terminator movie. There will also be another Marvel movie. Another Batman movie, another Star Wars movie, etc. Heck, they'll probably announce a Back to the Future remake soon with a time travelling iPhone that zaps you into the past when post selfies on Intsagram. I'm definitely not gonna waste my time getting triggered since unlike the Terminator. I don't have a power cell that lasts 120 years.