Russia eventuallly invades, how does Germany survive?

If Hitler were to somehow reach the decision to wait to invade Russia until his military was on a significantly better standing than it was, how would it have unfolded differently? Could Germany have prepared adequate defenses to hold out against possible Russian invasion whenever this would have been. What would this have entailed? Might it have been the case that if the Russians got passed the Vistula they would have been unstoppable?

If Barbarossa was to be carried out, would it have just been best for the Germans to have collapsed back to better positions after Kiev? Where would these positions have been and what would have been the plan? Most importantly, would Germany have been able to mount a successful long term defense had Hitler been willing? I'm assuming that after Kiev, inevitably all offensive operations by the Germans would become less and less beneficial/successful. Also, nothing the Germans could have done differently during Barbarossa would have been decisive enough and soon or later they would be forced onto the defensive.

I am thinking that unfortunately for Germany, nothing Hitler could have done differently would have stopped defeat by Russia.

Your thoughts on this are much appreciated.

Note: the most important question here is if Hitler had decided not to invade before the Russians did, how could Germany have dealt with this invasion. Whenever the Russian invasion would have occurred is up for debate.