I don't think there is any question of them giving up as long as there are investigative avenues to be followed. It would be unjustifiable.
Just because the Germans are sure of their ground I think that could be only one part of the investigation into Madeleine's case. There could be other associated lines of inquiry still being followed. We haven't a clue what is going on and that is as it should be; we are internet armchair detectives floundering about in ignorance while the real detectives are getting on with the real job.
I have never been interested in being any type of detective whether internet or real but unlike Wonderful Spam I didn't know from that first appearance of Madeleine's parents that they were guilty of being involved in their child's disappearance.
There was a point when all the ghastly and as we now know lies were being headlined and the being made arguidos when I did doubt their innocence.
However that was quickly dispensed ......and from then til now I have no doubt that Madeleine's parents are not involved in her disappearance.
It may be simplistic but my thoughts are that the weight of probability of Madeleine's parents being involved in her disappearance is rather less than the probability of a now known child abuser and rapist being in the vicinity of PDL.
Add to that the fact that both the UK police and the German police do not have Madeleine's parents as suspects.