Does Chinese have an adage saying “It is better to hit to kill than to hit and injure”?
Not sure if this is directly translated from the English or not but:


  撞死比撞伤强


And


  宁撞死毋撞伤


Or


  宁撞死 勿撞伤


I would go with the last one.

There's this Sina article from '06

交通肇事潜规则：宁撞死毋撞伤？
http://news.sina.com.cn/s/2006-12-24/123010849978s.shtml?from=wap

Talking all about it.

As for context, like the title of the article says above its really just a "unwritten" traffic "rule". I haven't seen it used in other contexts but I'm sure you could draw an illustration, especially just by tacking a -般 on the end.