these are very sensible questionand I can understand why you are asking them. If myunderstanding is correct then the ambient temperature of the Falklands is fairly cold so conking out would bring a whole lot more trouble than failing on the way to Yarmouth.
the more sophisticated an engine is the more likely it is to fail, so I'dsteer for a reliable and proven basic engine the three pot yamaha 60 - 90's are very reliable as is the V4 115. They are well engineered and providing properly maintained last for 20 to 30 years. they are also 2 stroke sothat means they are simplerto maintain and operate. The johnsohn that you have is a reliablengineI believe andtherea lot ofoldones around still
The reliability of an outboard depends on more than the engine type, the installation and operation is important as well. Fuel integrity is vital as is the electrical supply. To this end I'd consider running two batteries and twin fuel seperator/filters and devise a fueling policy and stick to it. Make sure your electrical works is top class and uses marine spec cable.
I have done thousand of hours almost all with engines less than two years old
and have had 6 failures. which was caused by
Honda 130 Split fuel tank (water in fuel)
Optimax225 6months old solenoid failure
Optimax 225 sameone but a few months older Oil pump failure
Optimax 150 18 monts old Crank failure
Yamaha70 Dodgy control cable causing intermittent revs
Tohatsu 90 Bag round skeg causing engine seizure
it's just as well im a good looking mutha cos I sure aint lucky!