I believe this law is covering deliberate assault, which is the context of Ex. As far as I can see, none of the other laws of vv. 12-26 would admit of an accidentally inflicted injury interpretation. Also, I have a problem of applying the death penalty to an accidental killing. I do not comment on all the specific possibilities such as you mention.
Ectopic pregnancy is a difficult moral problem.
I have heard arguments on both sides of what the moral duty is in such a circumstance. It may be, as you say, that abortion should not be given a special status as a crime, but only if it is understood that abortion is one form of premeditated murder. Finally, Calvin is not saying that the child is not alive, for in the same quote he speaks of the baby in the womb as already being a human being and as an infant that is killed by an abortion. All that he says, as I read him, is that it is a terrible crime to kill a child before it has the chance to enjoy life after birth. If you mean that we shouldn't assume that the unborn are not enjoying their life as it is in the womb, I agree, and don't think that Calvin would disagree either.