Exactly,the marines will get a huge L by allowing Luffy and Vegapunk to escape,but they will not be defeated.
I believe it will be made public that they were trying to kill Vegapunk, too.
If it's revealed the most beloved scientist in the world, who is literally responsible for people having lighting in their homes, Vegapunk, was targeted for assassination by the WG and Marines for investigating the Void Century, it would both cause interest in the Void Century, make the Marines look like giant lying assholes, and make Luffy, A YONKOU, look like a hero.
The Marines will lose ALL public face if Luffy is found to be the good guy here, and that he was trying to protect Vegapunk from the government murdering him.
This is like if the president of the US ordered the scientist who cured cancer to be murdered because he had discovered Atlantis and US corporations were scared of being challenged by ancient technology and wanted to steal it for themselves, and the scientist got saved by a group of random Somalian Pirates who happened to sail to his island just before it got invaded.
Imagine hearing this as, like, some goat farmer from the South Blue?
Also, many Marines were banking on Vegapunk's Seraphim replacing the Warlord's, meaning they'll be pissed, too.
This has the potential to be the single greatest PR nightmare we've seen in the entire series. Can't wait to see it blow up in the Gorosei's faces.