I suspect that will be a statistic that you will find in protected medical records as opposed to public records such as death certificates.
If you examine a death certificate , under the listing "Cause of Death" there are typically 4 or 5 lines with all but the last line appended with the phrase, "as a result of:" In the case of the man whose significant other administered a deadly wine enema of lore, if you check his death certificate I am willing to bet the coroner entered the cause of death as: "Acute ETOH(alcohol) poisoning." He may also have listed the contributing cause in item (2) in the list of causes to be wine. So the Cause of Death might read something like this:
Cause of Death:
(1)___Acute ETOH poisoning______________________ as a result of:
(2)___recreational injection of ETOH into rectum__ as a result of:
(3)________________________________________________as a result of:
I venture if you pull the death certificate you will find something similar to what is displayed above listed as the gentleman's cause of death without mention of the word enema. Doctors and officials will typically accurately describe a cause of death, but do so without utilizing verbiage that caters to the prurient interests.
So how would you go about finding statistics on death rates as a consequence of enema use? Well I would look for terms such as rectal perforation which is a well known risk with enema use. Another search string might be, "deaths resulting from hypertonic solution," or "renal failure induced by use of hypertonic solution."
Some info may be out there where enemas are directly specified as a cause of death, but it appears normally that such information is mostly of use of tabloids needing to sensationalize someone's misery for profit.