According to libertarian Professor Jeffrey Miron, the answer is simple.

Should health care reform cover illegal immigrants? For libertarians, that's any easy question:

1. Governments should not provide health insurance for anyone, so it does not have to decide whether to cover illegal immigrants.

2. Governments should not restrict immigration. Then all immigrants would be legal, so even if government provides health insurance, the immigration issue is moot.

You might not agree with either of points 1 or 2, but you have to admit that policymaking is nice and simple in Libertarian Land!