If not you ,I don't know What's to be done.语法有错么

If it is not you, I don' know what to do
如果那不是你，我不知道要做什么/我不知所措

当然what to be done也可以，就是复杂一些

没有错 不过 be to do 表将来时不太正式 will to be done 正式点

有错。
If it is not you,.....

if i lost you ,i don't know what i suppose to do.
如果失去了你，我不知该如何是好

If there aren't you