Is he serious? Has he already done the paperwork? When will it become effective?
Could you talk him out of it? What if you pay the difference in premiums?
Are you in school? Can you go talk to Student Health? They'll often offer a relatively inexpensive supplemental policy to cover what they don't.
Are you working? Can you get insurance through your job? Sometimes employers will offer insurance even if you're just part-time. I know Starbucks is like that. So is Walmart.
Is there a free clinic nearby?
There are the general questions I'd ask if we were sitting face-to-face. I don't know about anything that's specific for diabetics. But if there is something, I reckon the people here will know about it.
As a parent I understand his decision. I just recently took my 2 older children off my policy because it made our policy over $1000 per month. Now, as an unisured person you can seek out free or reduced price medical care. Also check out the insulin manufacturers for free or reduce price insulin. The government also has some high risk policies that may be available to you. Check out Home | HealthCare.gov for what is available in your state. Many diabetics are unisurered. I figured out our adult children were better off getting their own cheaper policies that using our very high deductible ($11,000)
Why would your Dad take you off his insurance at age 19? You can stay on his insurance until 26 years of age now with the change in healthcare reform. You are type 1 and that is not a smart thing to do; especially if you have no insurance of your own or are unable to afford. Why did he make this decision?
Like NayNay said your Dad can keep you on his insurance till you are 26 in most states. Ask him why he is doing this. Also there is free care out there based on a person's income. Don't give up, but find out the reason and then work from there. Wishing you the best. By the way, I don't have insurance either but do get free care and supplies based on my income. I am an unpaid caregiver.