Mishandling causes the fatallities not the situation itself...more often than not.
I have had 2 engine failures(+an inflight deliberate shutdown) in 'light piston twins' from mechanical/system failures of one kind or another. One in cruise and one just as the gear tucked up after takeoff, so I feel qualified to comment in both areas.
In the cruise case there was ample time to fiddle in an effort to gain some relief before it finally 'just stopped'...it was caused by multiple magneto failure. I was able to fly to an airfield and land 'normally'. I was in an Islander, 300hp variant.
The takeoff case was caused by a small piece of rubber fuel bladder blocking the uptake, momentarily and repeatedly, causing alternate full power and 'maximum quiet'
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At 50' with high trees coming up quick you decide which one is failing when the aircraft is yawing left and right!
I didn't have a 'dead foot'. Within seconds I had ensured Mix, pitch, pwr up...wheels and flaps up...and it yawed left first so I reduced power to that engine which improved the situation no end so I feathered left. This was in a C402A with only two pax and little baggage and it still took about 5nm to reach 500'...by then past the trees and over water.
What made the difference was training and experience...I was employed by a large 3rd level airline, Talair, which at the time was the largest airline of it's type in the Southern Hemisphere. Every 6 months we had to complete Base Checks and IR/Licence renewals to a high standard...or else...and we flew lots of sectors 6 days a week.
All our 402s and Islanders were OLD but generally well maintained...having said that we suffered engine (and a prop failure once) failures from time to time...the ONLY time fatalities occured was when a combination of DA and terrain made them impossible(or at best HIGHLY UNLIKELY) to survive type situations.
I've had several engine failure/forced landings in singles too. One after takeoff and I turned around and landed with the engine producing negligable power (C182)...one caused by running a tank dry at too low an altitude to effect restart, caused by confusion between myself and my trainee after I asked him to change selection but didn't check he had...MY fault!!
On that occassion I landed on a road downhill, downwind, around a corner in traffic and hit a power pole support guy wire about 50' above the road...which pitched us nose down at the last second before ripping out of the ground and doing some moderate damage as the bitter end with a (now) bent turn buckle whipped around the aircraft. We landed on our wheels and rolled to a halt.
This was in a C185. If I had gone for the tank selector straight away there is a strong likelyhood that the engine would have restarted and only a quick heartbeat result...HOWEVER...this aircrafts tank selector was out of sight between the seats and I was used to my OWN 185 which only had a firewall shutoff...no tank selector...so when ****s were trumps I reverted to what I knew best and the selector didn't occurr to me until I was on short finals to the road...and busy with missing power lines and cars, FLYING THE AEROPLANE...I elected to leave it when I remembered it because I was too busy flying the aeroplane..we hit the support cable a second or two later...if I'd been 'head down' fiddling with the inconveniently placed selector we may have died!
I've also landed a C206 blind after oil covered the windsceen in an engine failure...into a HUGE paddock using only heading and VSI info...the aircraft was badly damaged but I walked away without a scratch...because I flew the aeroplane.
So in which aircraft type was I safer?
Yes you are twice as likely to suffer an engine failure in a piston twin...but the chances of that failure happening at the worst moment...airborne and unable to stop/reland on remaining runway...are low indeed so a SE cruise/driftdown to an airport is entirely feesible.
Training and practice make the difference in the takeoff case...perhaps PPL/CPL holders should not be allowed to fly light piston twins unless they are prepared to spend the money on 'airline' style recurrency training or work for such a company.
I can gaurantee the bleak statistics for this category of aircraft would be dramatically better if this was the case...but an impossible situation to conceive of in a free democratic society..so we put up with the consequences which flow from that.
In the single engine case how often are you completely out of options for places where you can land survivably? RARE INDEED, and in most cases if you FLY THE AEROPLANE you won't even do significant damage to the aeroplane.
If we remove fuel mismanagement from the stats on SE forced landings it becomes a truly rare event...think about THAT!!!
Now think about how many SE forced landing events, by PPLs or low time CPLs end up tragically for NO REASON!!
The recent crash of a Cherokee 6 at Hamilton Is is a classic example....nothing short of the WING FALLING OFF is reason for a situation being unsurvivable for all or most of the occupants.
IT IS THAT SIMPLE!!!!
Talk of situations where operation is impossible, assymetrically, at significantly in excess of MTOW is stupid....no aeroplane will perform in those sort of 'ferry overgross' situations...no-one pretends they will, least of all the manufacturers...they were not designed too so they won't..simple!
If you're ferrying a light piston twin across vast oceans you're in a single engined aircraft until such time as you've burned enough fuel to be below normal weight limits...professionals who do this know it!
So which aeroplane type is safer?
They both are adequately safe when flown properly...I own a single engined aircraft and would not think of changing it for a twin simply because of engine failure considerations.
I could easily sell my Bonanza and buy a similar vintage Baron at no extra cost to purchase, probably even come out ahead...initially.
BUT I would double my engine maintenance and fuel bills for really no huge gain in 'safety'.
If I lived in a country where the weather was really bad a lot or was doing long overwater flights a lot I would buy the Baron or perhaps a C310 but here in Australia where the weather is severe clear 90+% of the time and we have plenty of 'wide open spaces', why?...when a little 'soft IFR' is required in my Bonanza a good hard look at the route and expected cloudbase enroute/freezing level is usually all that is required to give some extra margin for the rare case of MECHANICAL FAILURE.
I don't fly IFR/night SE over tiger country or in severe weather...I wouldn't in a Baron either...it's no more likely to cope with severe turbulence/icing than the Bonanza.
I have flown over SEVERE tiger country(PNG) in piston twins (BE65/C402/404/Aerostar) IFR and in IMC for many thousands of hours...now I don't have to I chose not to...that's what Transport Cat aircraft are for...the ONLY AIRCRAFT with GAURANTEED PERFORMANCE.
Chuck.