Sue for what?
In any case, what difference would that make? FIFA suing UEFA wouldn't have any bearing on Germany etc... leaving FIFA. In fact, it may do further good in terms of dragging UEFA down with FIFA and Platini down with Blatter.
It's not a case of Germany leaving Fifa, they are proposing that Uefa leave Fifa which would obviously mean us as well. They don't seem to be proposing some sort of unilateral action. If Uefa went it alone then Platini would, as it stands, be in charge of the breakaway group.