The image of Hitler has been incorporated into the design of many Nazi German posters between 1927-1938; however, he only features in one definite poster that I can find between the actual years of WWII. This 1943 poster, which was recalled following the loss at Stalingrad in February, is found in the Bundesarchiv: 'Adolf Hitler ist der Sieg!' (Adolf Hitler is victory!).
I am completing post-graduate study on Nazi propaganda poster art and its contribution to the development of the 'Hitler Myth' concept through the use of Hitler's image and text i.e. 'Führer'. I am analysing 45 posters between 1927-1938, and have only found one (potentially two more) available for 1939-1945.
My current assumptions are that Hitler had established power and self-promotion was no longer crucial, a prioritisation on the propaganda war themes of enlistment, homefront sacrifice and enemy threat following 1939, a focus on anti-Bolshevism and 'total war' following Goebbels' 1943 speech, and a decline in the popularity of Hitler's leadership following the decision to throw the country into a second world war. However, this does not explain the unexpected incorporation of Hitler into 1943 poster art.
A Boston College affiliated database does show two potentially additional posters, http://www.bc.edu/bc_org/avp/cas/his/CoreArt/prop/ns10.html, which I cannot verify due to links leading to 'Page not found' and their lack of appearance elsewhere on internet datatbases.
Regarding your general assumptions that,
Hitler had established power and self-promotion was no longer crucial, a prioritisation on the propaganda war themes of enlistment, homefront sacrifice and enemy threat following 1939, a focus on anti-Bolshevism and 'total war' following Goebbels' 1943 speech, and a decline in the popularity of Hitler's leadership following the decision to throw the country into a second world war.
I'm not sure you can safely assume this generally, and the decline in popularity of Hitler would require some substantial evidence as it's certainly not broadly believed to be the case. While I can't speak for posters, the Hitler myth and the overt display of Führerprinzip was as present after 1939 as it was beforehand - perhaps even more present than beforehand - within cinema. The image of Hitler was invoked both directly (see this newsreel and this newsreel for a typical example, although there are plenty more) usually focusing on his characterization as a genius military strategist and his victories in the West, and indirectly through films focusing on 'great men' (usually from Prussian history, most notably the figures of Frederick and Bismarck) such as Bismarck (1940), Die Entlassung (1942) and The Great King (1942).
If you're at all interested, David Welch's book, Propaganda and the German Cinema, 1933–1945 (2001), which covers the methods of German film propaganda pretty decently (and was my entry point on the subject), has a section entirely dedicated to Führerprinzip in film. Keep in mind he is extremely focused on cinema's manifest political function, believing that all Nazi cinema was effectively part of an organized propaganda effort, and so unfortunately doesn't touch on popular cinema, public reception, economic considerations, etc. He's also seemingly dismissive of incorporating film theory into his work, which might be a blessing or a curse depending on how you feel about it personally.
He's also written a book on Nazi propaganda more generally, The Third Reich: Politics and Propaganda (2002), which might be more useful to you but I've only read the section dealing with film - which is almost a word for word rehash of his other book. (Seriously, it's a little bit slack).
^Also, ^I'm ^unsure ^whether ^this ^will ^be ^removed, ^but ^I ^promise ^I ^checked ^the ^rules ^first, ^mods! ^I ^can't ^tell ^whether ^this ^post ^is ^allowed ^because ^I'm ^addressing ^a ^statement ^made ^by ^OP, ^not ^the ^central ^question.