Let's break this down because MA laws are a bit different than those of most of the country.
Although MA has probably the most employee friendly laws in the country when it comes to both health insurance and holiday benefits, even MA laws do not require ANY employee, either full or part time, to be paid holiday pay if the office is closed. Any EXEMPT employees must be paid when the office is closed (unless they do no work at all for the entire work week) because Federal law limits when an exempt employee can be docked, but under no state or Federal law does a non-exempt employee have to be paid when they do not work. Whether the office is closed or not. Whether it's a holiday or not. Whether part time employees get holiday pay when the office is closed is ENTIRELY dependent on the employer's policy. It is NOT required by law.
As regards health insurance, this is a matter of BOTH law and the insurance policy itself. Under MA law, if the employer has 11 or more full time employees, they are required to provide health insurance to those employees. Full time, for health insurance purposes ONLY, full time is considered 35 hours a week (note to future readers - this is a MA state law that applies only in MA - do not write to us complaining that your employer in Nebraska or Colorado or even New Hampshire is not offering you health insurance and you work over 35 hours a week - the definition does not apply in your state). So if your employer has 11 or more employees AND you regularly work 35 hours a week or more, your employer MUST provide health insurance.
However, if your employer has 10 or fewer employees OR you work under 35 hours a week, your employer MAY provide health insurance but is not required to under the state mandate. In those instances, eligibilty for health insurance reverts to the insurance policy. Your policy will indicate who is an eligible employee. If you meet the definition of an eligible employee under the policy definition, your employer must offer you the insurance - if you do not, he needn't.
If your status changes and you are no longer eligible, you can lose the insurance. So if you've been working 35 hours a week regularly, but the employer loses business and cuts your hours to 20 hours regularly, you are no longer eligible and you don't get the insurance any longer. That doesn't mean that if you only work 20 hours for one week, but then go back to 35, you won't be covered for that week. But if your hours are cut on an on-going basis to less than the minimum defined in the policy, then your employer is not obligated to provide the benefit.