Using gas turbine engines in helicopters was an enormous improvement, because the power weight ratio of gas turbines is so much better than that of piston engines. It is doubtful if you can approach the power weight ratio of piston engines with a combination of fuel cells and electro motors any time soon. This will not be compensated by a lower fuel consumption.
There is a place to achieve an additional advantage. The gears between the engines and the rotors are vital, complicated and heavy. Those between the electro motors and the rotors might be simpler and a little less heavy.
All together: wait for fuel cells to find application in light propeller aircraft before thinking about using them in helicopters.