I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
The wisteria problem is very strange. Some possibilities include a soil root rot. These are usually brought on by soggy soil conditions although not always. Over saturated soil can exclude oxygen from roots and result in death of many types of plants. If the entire plant died that suddenly it is likely a root related issue of some sort. When you dig it up see if there is a nursery tag or encircling root or some twine or similar material strangling the trunk just below the ground level.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
Q&A Library Searching Tips