How do you say "goodbye ill miss you" in german?
Auf Wiedersehen, ich werde dich vermissen.
as well as Ich vermisse dich/Ich vermisse Sie, you can say "du fehlst mir", which is quite a nice and perhaps romantic way of saying the same thing.
Or Auf Wiedersehen, ich vermisse (or misse) dich, as the Futur tense is not used regularly in German; it's covered by the Prasens.
@janowskima, DeanO: In order to convey exactly the meaning the original poster asked for, you have to use the futur tense in German as well: 'Ich werde dich vermissen' or 'Du wirst mir fehlen'.
How do you say 'I miss you'? ... du fehlst mir. ??