I think the idea that you have twice the chance of a failure in a twin has grown from the conception that as you have two you have two engines to potentailly fail which doesnt mean twice as likely to fail.
One safety factor of a twin which is often missed is that the engines are on the wings rather than infront of you as in a single.
Aircraft design is attrocious regarding crash protection and a head on with a single on ground contact inevitably means that giant lump of metal in front of you joins you in the cockpit!
Normally aspirated twins do have a poor single engine ceiling but something like a Seneca Five turbo charged intercooled unit has a service ceiling single engine of 16500 feet which is pretty good.
Pace