Proper operation with an AOC, two professional pilots, Multi engine aircraft. MINIMUM
If you want scheduled airline safety standards, that.
Single pilot increases the risk. Single engine increases the risk. Flying single engine at night increases the risk a bit more still (though I'm not convinced SE over land at night is materially safer than over water). All this should be properly explained to any prospective SLF.
But the PA46 was designed for this type of mission, if flown on a sensible flight plan by a properly rated pilot. It's deiced & has just about as much redundancy as you'll get in an SEP. A quick climb to the lower airways, out of the ice, well before the open water segment. A controller keeping watch who knows precisely where you are, and should the worst happen, can coordinate S&R assets without delay.
Forecast icing at the planned cruise level, no go.
Off airways, low level at night over a freezing sea, no way.