Comment by Yizahi

Proper (most) of the facilities which do this require people to stop drinking for at least few days before procedure, and some offer paid service isolating patient for a few days under supervision, and then do a block. In cases when patient is already delirious from intoxication these facilities can force one to go cold turkey, but at the same time put patient on the IV with some supplements and issue anti-psychotics (by doctors of course).

So in general the system is well equipped to not allow patients die from abstaining.