[Longhanks]

Once the people choose to no longer follow the EU Supreme Court, thus, as a follow up, no longer choose to follow the EU treaties, they exit the EU just as the UK did.

No country is or can be forced to be a EU member.

Just because there are economic implications does not mean the EU treaties are above the countries‘ constitutions the people actually chose to enact.

[SiempreViernes]

This is true of any law, there isn't actually anything except common agreement that constitutions should be treated more seriously giving them extra status, and there isn't anything but the consent of (enough) people giving laws any power: nobody is ever forced to follow any law, they are simply punished if they don't.

However, once you decide to stay within the law it is indeed possible to have EU treaties stand above the constitution. In situations where you've added bits in your constitution that the EU treaty has priority, acting like this isn't true is simply breaking the law.