Realistically speaking, it has to not involve any of the Strawhats dying, turning coat, etc.
I just don't see things going well for them at the Raid, as they failed to account for Big Mom. However, we're already made to think the crew and allies are trapped and incapable of aiding Kin'emon and co due to Orochi destroying the bridge, but that's just isn't enough of a crisis.
One idea I have is the SHs and allies managing to get to Onigashima and causing a bunch of commotion. This culminates with them eventually getting overpowered and forced to retreat. During the process, one of them is captured and given a SMILE. There's panic from the rest who escaped, thinking they've lost a crewmate to Kaido and Big Mom. There's infighting, and even some beginning to lose faith and walking out. Luffy and few others stay the course and continue on for the attack.
From there, lots of other things could happen, like more allies such as the Sun Pirates, Germa, and Grandfleet arriving to lend an aid, and G5, along with Vegapunk, coming with cures for SMILE.
