If two parties sign an agreement and one party can prove that the other party did not demand that the terms be enforced when it could have, can the other party argue that the entire contract is void and unenforceable because the parties never intended to enforce it in the first place or due to waiver?
For example, an employee was initially hired for a one year term at $50 an hour after which the employee transitioned to an at will employee. The employee continues working for the company for several years. After a few years the company renews the employees contract for 8 more years at $75 an hour but continues to pay the employee $50 an hour and the employee never demands the higher salary. Let's further assume that the second contract contains several other benefits for the employee but the employee continues to act as if the first contract is in force. For example, the first contract did not provide dental insurance, the second one did and the employee never demanded dental insurance.
Suppose the second contract contains certain provisions that the employee wishes to enforce during his 7th or 8th year of employment.
Can the employer argue that the entire contract is null and void since the employee never enforced the other provisions of the contract? Can the employer argue that the employee "waived his right" to the second contract by not enforcing it and acting as if it never existed?
Are there any case precedents that can be applied to prove either way?