Let nature take its course. 顺其自然。（这种表达有点哲学态度的意味，比较积极一些。）Let it be. 随波逐流，让它去。（这种表达有一点点随便放任的态度在里面。）
Just let it go
let it be it is.
let everything go the way it is
Let nature run its course
