re: Knowing What we Know now, does Gavrilo Princip pull the Trigger?

Some form of WWI would have happened eventually without the assassination.

Whether the Romanovs would have survived in Russia is questionable, and if not, would the Bolsheviks have been able to co-opt the replacement government as they did is subjective. Probably not.

Germany's fate is interesting to ponder, events could have broken many different ways, some better for them and some worse.

Ditto for France.

The U.K. loses Ireland in many other scenarios? Don't think so.

The U.S. was the clear winner after WWI, maybe not as much in other scenarios?

Sadly, larger scale, the unresolved issues from WWI led directly to WWII, too bad that drama played out as it did. We'll never know the answer to your question.