After engine ignition, isn't it pretty much that success or massive explosion are the only outcomes?

Nah engines are able to turn off after ignition. Thats what the Raptor safety is. Usually the blow or moment is when it lifts off the tower with one notable exception that I know of.

https://en.wikipedia.org/wiki/Mercury-Redstone_1

Technically the Shuttle go or blow moment is when the SRBs are turned on.

But yes, otherwise in the spirit, it will either blow up or be generally sucessful.

So you are admitting that what Musk meant was they had a 2/3s chance of an explosion.

So you’re saying that if the engines had been off the starship wouldn’t have exploded? Try again bud. That’s still an object full of compressed methane and liquid oxygen falling at terminal velocity.