What I can't understand about the war is why exactly Rayleigh did not go to help ace. He at least was able to stop kizaru during the SA events so he obviously would have been a major asset to the WB pirates had he tried. I just can't understand why he did not go to help the son of the man he served as VA for 30 years.
Rayleigh clearly showed that even though he himself was
extremely close to Roger that at the same time he didn't owe anything to his son. Roger obviously didn't leave Ace with Rayleigh for a reason, which was most likely because he didn't want him hunted by the WG and Marines. But at the same time WB had taken over as Ace's "father figure" after Garp of course. And yeah even though Garp didn't literally raise Ace, he looked out for him as long as he could and did his best to keep him safe. Point being is that Roger appointed someone to look after his son, and then another man took that position with Ace's consent, that being WB. So i'm sure that in Rayleigh's mind it just wasn't his place to be involved in this matter. Also Rayleigh wasn't really Roger's First Mate for 30 years. It was probably at best, 15 or so years. Especially since Roger and Rayleigh seemed to have been in their early 20's when they
first met. And Roger himself has been dead for 25 or so years now.
But in terms of how this war would have resulted had the RH Pirates fought along side of the WB Pirates. I don't think that there would have been a decisive winner at all. For the simple fact that other then Akainu, Aokiji and Kizaru were basically unchallenged all war long. They waltzed through the war rather effortlessly and in all seriousness they could have easily crushed most of the WB Pirates had they really gone all out. And then Garp and Sengoku definitely seem to be guys who can put up a hell of a fight if need be as well. So those two guys could probably tear it up on a good level also. Then even guys like Kuma, Donflamingo, and Sentomaru also went rather unchallenged all war long as well. So had all of them gone all out i think that the RH and WB Pirates would have had their hands really full. The "top dogs" from the Marnie's side, other then Akainu, really didn't seem to go even close to "all out". While everyone of WB's side definitely went all out to save Ace. So even with the RH Pirates winning that war would, in my mind, have been a toss up.
Also i'm not taking into account the BB Pirates showing up, because for them that would have been utter suicide at that time with all of those powers assembled there.