Burning it at the source means thatuch more gas will also be extracted and (ultimately) burnt for the other use.
2xNH3 -> 3xH2 + N2 is fine, only excepting that more NH3 will need to be made. In the future it will be made with wind or solar energy, but that is still a few decades off.
For instance, nitrogen fertilizer eventually breaks the hydrogen bonds and ends up back in the atmosphere.