I am not sure about there being ‚evidence‘ for MMs death. Upon cursory review of the German press, I have not come across this type of definitive wording, at least.
As for photographic evidence, I‘d just like to mention that in the Zanvoordt files investigators talked about ‚look alikes‘ all the time, when relatives believed they had identified their missing daughter or sibling or...
Equally, when Noreen Gosch identified her son on photos (even pointing out birth marks), investigators dismissed that, too.
(There are indications that in both instances investigators were not invested in finding the truth, so this might be different here, hopefully, at least as far as German police is concerned).