Anyway to try and actually answer the questions posed.
1) Could different union leadership have avoided the strike?
Possibly. The Government were gearing up for a fight but well so were the unions (see Scargill's quote about hitler where he promised to fight the tories in any way possible) and a less combatative union might have delayed the problem.
But well a) the government were planning more pit closures then they said they would do so even if they bought peace there, the reaction would just be worse when it actually happened and b) it wasn't scargill who started the strike, it was local guys in yorkshire, scargill was reacting to that which indicates a certain overall trend.
2) Could different union leadership have forced the government to come to terms?
Yes. Without a question, yes. McGregor has gone on record that he would have capitulated if NACODS had carried out their planned strike action as well as NUM. You just need to avoid that to get a striker victory.
3) If Scargill had held a national ballot would he have managed to get the support he needed, from NACODS if nothing else, to force the government to terms?
Possibly. I'm not convinced it's the smoking gun many think it is.
For a start, the delegates voted against having one so it'd be anti-democratic in a way to go back on that (though you'd assume that Scargill supporting it might swing some voters). And well what if he loses? He might well have done. Which rather kneecaps any response he can make.
If he had held a national ballot rather than local ballot, the strike wouldn't have been declared illegal but the strike was only declared illegal when it was forced on areas that voted against strikes by the flying picket lines not in other areas. But you'd still have the violence and the general sense that the public were tired of strikes so I'm not sure public opinion would be that different.
4) If the miners had won, what then?
It'd just delay the reckoning. You can, and should, criticise all sides for how it was handled but so much of the result was inevitable and I think if the miner's do win, there's just another day further down the line when they don't. The refusal to accept any more mines closing, after how many they'd lost already, just meant they decided to be hung together rather than seperately.