This is called nondiscrimination. All group health plans in Arizona must limit exclusion of pre-existing conditions. There are rules about what counts as a pre-existing condition and how long you must wait before a new health plan will begin to pay for care for that condition. Generally, if you join a new plan your old coverage will be credited toward the pre-existing condition exclusion period, provided you did not have a long break in coverage. Your health insurance cannot be canceled because you get sick.
All health insurance is guaranteed renewable.
If you leave your job, you may be able to remain in your old group health plan for a certain length of time. If you work for an employer with 20 or more employees, it can help when you are between jobs or waiting for a new health plan to cover your pre-existing condition. There are limits on what you can be charged for this coverage. I believe that having health coverage though your former employer counts as creditable coverage. Consequently, you will be treated as if you have changed jobs.