BOAC
Yes, you're right...worrying is sensible. I should have written my sentence more clearly. The worrying should be before the takeoff....not after, when it's too late. When you're out of airspeed, altitude, and ideas is not the time to wonder 'what if'.
I flew for a major carrier in the U.S. In the U.S., it's against the law to takeoff when, after a takeoff an engine fails, the resultant climb gradient is insufficient to safely continue the climbout.
In fact, our routing across the Rockies depended on our weight, temperature aloft, and the resultant drift-down performance. In cases of relatively heavy weight, ISA plus XX, etc., our dispatched routing was specifically filed for those conditions....and the unlikely event of an engine failure enroute. If ATC were to offer to us 'Cleared Direct to XXX', we were not necessarily legal to accept it....even though it saved time and fuel.
Can't speak about your airline or your country. Frankly, I'm ignorant.
But, I can say with confidence, in the U.S., in the event of an engine failure, you have to be able to clear the terrain or you change either your routing, your weight, or both. This applies to all phases of flight.
Fly safe,
PantLoad