You can sign up for ATT fiber business class and they install a second line to your home right longside sonic/consumer ATT fiber. You pay 99 for install and get a second ONT, second fiber line installed and gateway which is kind of a waste. But you can then cancel sonic, save $30-40 per month and have no downtime and switching from business fiber to residential is easy with no contact/lock-in.
Remember, no data caps with ATT anymore and HBO is included with no landline requirement.
Sonic dropped the ball here. All they needed to do to keep customers was fix their contract with ATT