I can’t help much with advice cancelling Vivint, but it looks like the other user here gave some suggestions. This thread discusses a similar question.
Regarding the sensors, if you have an older GC2 and not the Sky panel, you definitely have the 10/20 series standard 2GIG sensors, there wouldn’t be a compatibility concern.
You could reuse the sensors with the Qolsys 345Mhz version panel.
There is no need to remove them from the GC2. Those 345Mhz sensors just broadcast their signal and the panel is programmed to listen for it, they aren’t two way communication devices like Z-wave or PowerG.
You should be able to reuse all the sensors you listed. If you have a TS1 secondary touchscreen it would need replaced or discarded as it would not be compatible.