Always be ready for the worst. That's what they were taught.
That's why they always kept a few guns in the car.
That's why they kept a first aid kit in every room in the house.
That's why they stashed a few thousand dollars in several different places around London.
That's why, when Jim died, they had a fallback.
They knew something like this would happen. Just the kind of man Jim was.
Unstable. Volatile. Mercurial.
That's why when they heard the shot and saw him lying dead (they were watching from separate rooftops, of course) they ran for it.
Each collected one of the packets of money and met with the other at their designated location. Together they had passports and ID's forged, names changed, hair dyed.
They each went their own way. Twins divided. To opposite ends of the earth.
They agreed to meet each other back in London in 3 years time. To give things a chance to settle. To calm.
It all goes perfectly. Without a single hitch.
Until they return to London. Until they reconnect.
Until they discover that the detective is still alive.
They load their weapons.