Helicopters only have an "avoid curve" if they are either single engined, or twin engined above a certain weight. Therefore the answer is to fly twins at an appropriate weight which, with some modern types, can be close to max all up weight.
Alternatively, consider just how much risk there is of a gas turbine engine failure. For aerial work over non-congested areas it is probably better to spend the money on top notch maintenance, HUMS etc rather than on the extra cost of a twin. After all, if you eliminate any risk from an engine failure, helicopters and their pilots have a habit of finding alternative ways to crash.
Airships have been around for a long time. If it were advantageous to use them, I sure that would happen. They are not used in these roles for a good reason.