这两个不一样：
went away 是go away的过去式:
vt.离开(走掉)
I wish he'd go away; I can't stand the sight of him.
我希望他离开,我讨厌这个家伙.
is away也是be away的一般现在时的变形:
离开
In all likelihood,we shall be away for a week.
我们很可能离开一个星期.