Go under the knife

To go under the knife is to have surgery.  

“After the accident he had to go under the knife to repair his broken leg.”

Go to seed

If someone or something has gone to seed, it has declined in quality or appearance.   

”The old neighborhood has gone to seed.”

Go-to guy

He is somebody who can be relied upon for help or support every time.  

“My brother is the go-to guy in his class.”

Go through the roof

To go through the roof is to lose one’s temper or become very angry. (‘Hit the ceiling/roof’ is also used.)  

“The manager went through the roof when her secretary resigned without prior notice.”

Go scot-free

If you go scot-free, you escape the punishment you deserve.  

“The suspect went scot-free after the complainant submitted a desistance.”