Personally, I'd prefer if they didn't get any outside help. Like, "WG accounts for all of that yet Mihawk still holds the fort" (yes, I'm a fan).
I'm not saying two admirals going down to Mihawk, but if Mihawk, with Croco's backup, makes them order retreat that's more than satisfying enough.
If someone has to help them then... either Shanks, or Perona arriving with Moria (who, of course are no top tiers, but both their powers are strong nuisances). They don't have any more friends than we know of. I was thinking Weevil if they fred him but I don't know why they would go that far for him.
Do we know of any more connections?
I'll google the flashback, that part is interesting.
I'm not taking the Bullet = Rayleigh stuff seriously since he was a villain prior to CoC coating and G5. I couldn't take Shiki seriously for similar reasons.