The issues with Cavani and Gameiro weren't that they couldn't play wide, although it was clearly not their best position... Firstly, it was that Ibra dezoned everywhere and they ended being lost a lot positionally. And most importantly, Ibra would get demonstratively angry if he didn't get the ball. Ibra was the star on the attack, so the other players and the manager complied. Those two got very few touches when they played with Ibra. Hard to do anything when your touches are very low and you're not playing instinctively.
That's what I'll be looking for with Martial. Is he going to get his touches? Will he float positionally because Ibra is dezoning all over the place? The advantage Martial has over the aforementioned is that he is much better technically and he can run with the ball at his feet (in fact he prefers it). The other two relied on movement and making precise runs... they weren't able to.
I think Mourinho is a strong enough manager to force Ibra to play more for the team shape and less for his own personal comfort. But we will see. I don't think it will be that easy. If Ibra doesn't get the stats or the notoriety he craves, he will force the issue.
I will say that I think Martial has a good chance of working out with Ibra. But I am concerned. It's not easy. The partnerships with other strikers at PSG did not work at all.