Oh yes there is a strong corrolation between miscarriages and other problems, especially blood clots. In fact, most doctors you talk to will know the connection between blood clotting disorders and multiple miscarriages but not between it and PE (since a lot of woman with them end up with the miscarraiges instead of PE because they don't get that far along).
Having multiple miscarriages is enough reason to run a full set of blood work on both clotting and autoimmune issues.
As for post partem PE, well delivery isn't the only cure, time is as well. You could have clots in places other then the placenta (blood clots), there may be residual eneimes left over that your body is attacking (auto immune), hormones can still be out of whack (this can affect everything from clotting, autoimmune to toher conditions like PCOS, diabetes etc..).
Not only do you have to deliver, but you also have to have time pass for whatever is cuasing the PE in the first place to start to correct itself. For some it takes a matter of minutes, others it can take weeks and for some of us it can takes months or years for our bodies to come back to normal.