They'd still be profiting from animal cruelty, whether or not they initiated it. Even back in 1979, Coppola caught a lot of
![[censored]](https://debrief.commanderbond.net/topic/34716-cobra-mongoose-fight/style_emoticons/default/censored.gif)
for using that cow chopping thing, even though he didn't arrange it. The problem is that he exploited it for financial gain. I don't entirely agree with that logic, but there it is. And even assuming the producers have no compassion for animals whatsoever, I doubt they would risk breaking any labor laws or safety codes. Such a fight, if real, could result in an extra being injured, and unlike animals, extras can sue.
Anyway, a real fight might actually be less entertaining than one contrived using special effects and creative editing. A real fight might be repetitive and boringly slow. On the other hand it could be ridiculously fast, a blur in the corner of a shot. No one knows until it's over. Perhaps the animals would refuse to fight or one would escape. These are animals, not actors, and they can't be controlled. What if one of the animals expired without contributing a usable take? Would they buy ten cobras and ten mongooses just in case? Producers don't like vagaries like that. When you stop and look at all the contingencies, faking it would be the only option.
With a little imagination, a realistic
and entertaining effect could be achieved. Just as a guess, perhaps they filmed the animals separately, each attacking a little green prop or something, and then digitally combined the images. Perhaps the mongoose was real and they used a mechanical snake augmented by CGI. I don't know. But however they did it, you can be sure they didn't just throw the creatures into an empty swimming pool and film them going at it.