Losing the control over the vehicle in a fast corner is easy. It is even easier when the truck has only two axles and therefore it is less stable. Sometimes you only take the wayside or hit the barriers which is not a big deal.
But sometimes other things happen. Remember that damage may be significant and the engine may stop working or the truck will not react as it should.
In such moments you have to call the emergency road service. To do it, use the Route Advisor, select a proper tab and click on a button ([Enter] by default).
The help will automatically take the truck and trailer to the closest city. You will pay for that and you will lose some time (depends on the distance from the city).
You will be brought to a car repair shop. Here you can fix your engine quickly and move on. Remember that you cannot repair damaged cargo.