First and foremost, a sane dose of any benzo will not have a tremendous effect on your heart. But they do reduce you mental awareness of dangerous activities. (Overdosing on Cocaine) Secondly, good coke is very easy to overdose on in quantity.
Billy Mayes died of a combination of the two, but his cocaine addiction and heart disease was to blame. (A hidden one and very bad one at that.) With his judgment lapsed on heavy doses of multiple benzos he tooted some coke in combo with oxycodone, hydrocodone, Tramadol, Xanax and Valium. This would kill anybody.
His death was more attributed to his untreated hypertension. Cocaine was a contributing factor.
Benzos are more of a mental edginess type drug. They are used for stimulant psychosis all the time, even in combination with anti-psychotics.
If used on occasion this combo is safer than getting really drunk or smoking cigarettes by themselves.
The only problem with cocaine is that it is really easy to dose again too early, leading to a build up of it. You dose too soon too often, and you will die in a very painful manner.