So...there are multiple ways how this can play out:
1) We get some Enies Lobby style war and no outside help comes, so a lot of power ups or techniques we have yet to witness (possible since they all had a lot of time to prepare for the war) will come into play. Kidd or Law would likely take on Big Mom in that scenario. There is also the possibility Toki did something like storing all the experience Momo would have gained had he lived normally and releasing it when the right time has come.
2) They will get outside help like Weevil, Marco or the Navy. The first two would prolly join the alliance directly while the latter would help indirectly. Koby and Drake would then join the fight.
3) A combination of both. Like they will get some help, but the current alliance will still take over most of the fighting.
1) We get some Enies Lobby style war and no outside help comes, so a lot of power ups or techniques we have yet to witness (possible since they all had a lot of time to prepare for the war) will come into play. Kidd or Law would likely take on Big Mom in that scenario. There is also the possibility Toki did something like storing all the experience Momo would have gained had he lived normally and releasing it when the right time has come.
2) They will get outside help like Weevil, Marco or the Navy. The first two would prolly join the alliance directly while the latter would help indirectly. Koby and Drake would then join the fight.
3) A combination of both. Like they will get some help, but the current alliance will still take over most of the fighting.