Yes that is absolutely right, as per the agreement that was collectively bargained by the Players' Association and management. If he doesn't like those terms, he should speak to his union representative. He is also perfectly free to find some other profession if he thinks he is being treated unfairly. He cannot go to the 49ers or Cowboys, but he certainly can go work for McDonald's if he would like.
In contractual law, there's no such term as "everyone knows." It's either in black and white or it isn't.
The Cowboys have every right to keep Romo at his 2018 number of $19.5 million without making any promises for 2019 or beyond. They also have every right to cut him and (I believe) owe him nothing. I would not begrudge them choosing either of those 2 options. Certainly there is the possibility of a mutually agreed renegotiation. However, Romo also has every right to say "I won't renegotiate so you either pay me $19.5 million in 2018 or cut me" (and I would not begrudge him that right).
What would upset me would be if the Cowboys say to Romo that they want him here in 2018 and will pay him $19.5 million and Romo refuses to report and is unhappy with that deal and demands a trade. However, everything we know about Romo's personality suggests that would not happen.
Don't be ridiculous. If the Vikings exercise their option to keep him, they certainly have to pay him accordingly. I believe it is $13/$15/$17 million respectively. That's their end of the bargain.
He freely and willingly signed a deal whereby he got $36 million guaranteed and roughly $50 million by 2014. As per of that deal, which he freely and willingly signed, he knew he would have little control of his situation between 2015-2017. He's just another spoiled athlete who gladly took all the upfront money, but is now complaining about having to fulfill his end of the deal.