As an outsider, i'd like to offer the following.....
Single engine.....fire goes out, you're going down.
2 engines....TWICE the probability of engine (or extra transmission components, V a single) failure BUT at least you have one Donk, albeit it's lugging the weight and drag of the dead 'un, to give you a bit of flight TIME in which to find a landing-site.
I see no relevance in the reliability issue, provided we're comparing an apple with 2 apples......it's a different and pointless exercise to compare 2 apples with one orange.
Twin adds a margin of extra safety, but at a horrendous financial premium.
Single is a fraction of the FINANCIAL cost, but what value lives, families and pilots.
Nanny state makes that decision for us.
Perhaps the penalty of wide-spaced landing-gear, with rigid, streamlined floats, could be an option for single-engine over-water ops?
Of course, even then, sea-state would have a big effect on outcome....but twins still ditch and people still die......