"70V audio lines" are typically only for commercial PA applications
with speaker distribution systems (e.g. installed musak in a store),
and wouldn't be involved here, as we're on the input side of the PA.
However, phantom power, a DC standard of 48V for biasing electret
condenser mic capsules, is extremely likely to be present on the
3-conductor XLR cables that are used with PA systems. If there is any
current limiting in their design, it's in excess of an amp iirc.

--

Electrocutions and shock hazards have been around since the very early
days of sound systems. The old amplifier designs were more likely to
present a hazard, but anything connected to directly to the power
mains with a hardwire cable can also present a hazard. The hazard is
greatly increased if water is involved. Broadcasters have known this
for years.

A conventional wired microphone has either 2 or 3 conductors, one of
which is always supposed to be grounded to minimize noise pickup from
stray electromagnetic fields. If there is a fault in the amp or the
power supply wiring, it is quite easy to have the microphone ground
become a live AC mains "Hot Wire". Apparently this is what happened
to the preacher and the current passed through his body into the water
which was at or near ground potential.

As has been said before, an inexpensive RF mic is the way to go in
these situations.

Beachcomber