I’m sorry that you have a significant problem in your garden. The fact that there has been such a drastic change in three different species of plants suggests an environmental change of some kind. Four possibilities include contamination or alteration of the soil in some way (such as by the addition of a chemical contaminant or too much water), infection by parasites, attack by pests, or more than one of these problems. Soil problems can sometimes stimulate parasite growth.
As far as English ivy is concerned, I know of four situations involving parasites that can cause serious problems. A fungus called Rhizoctonia Solani causes root rot. The fungus can affect many other types of plants besides English ivy. Bacterial leaf spot is caused by bacteria in the genus Xanthomonas. Anthracnose is a disease caused by various kinds of fungi. Phytophthora is a water mold that can infect ivy.
A garden expert would need to examine your plants or soil in person (and perhaps in the lab) to identify the specific problem in your garden. I don’t know whether the plants will be able to grow back after such severe damage.