So, the information on wikipedia, or at least in the German version from the article, comes pretty much from the only source that ever bothered to collect the dates of death of former perpetrators on a large scale and that all wikipedia entries for less well known people in that category use: Ernst Klee's Das Personenlexikon zum Dritten Reich., which compiles about 4300 short biographies of important people in relation to the Third Reich and was first published in 2003.

Klee is generally a reliable source and while I, back when I worked extensively with that book, found some inaccuracies, if you are just looking for a citation on the date of death, Klee is the way to go. The 2001 date of death is also backed up by the biography of the Auschwitz Trial exhibition, which is maintained by the Fritz Bauer Institute, a highly reputable institute doing research on the Third Reich and Nazi Trials and named after one of the the people responsible for the Auschwitz trial.

If you want the best and real confirmation, the way to go would be to write an email as well as a letter (letters are better in this case because they are viewed as more "bureacratic") to the Standesamt Waldsassen, which is the agency collecting birth-, death-, and marriage-certificates and where you need to explain your project and apply for access to the death certificates since they are only given out if there is proper scientific interest because they fall under personal privacy laws in Germany.

I can also tell you that if the Waldsassen and 2001 information is correct (and there is a very high likelihood it is), Bednarek didn't die in prison. The reasons for that is that there is no prison in Waldsassen, and that Bednarek was imprisoned in Butzbach in Hessen, and that life imprisonment in Germany means usually release after 20 to 25 years.

As for newspaper obits, that gets a bit tricky. Waldsassen has from what I can tell three newspapers that cover it: The Oberpflazer Nachrichten, the Augsburger Allgemeine and as a national newspaper that strongly covers Bavaria, the Süddeutsche Zeitung. The Oberpflazer Nachrichten do not have an online archive dating as far back as 2001 it seems, and the same is the case for the Augsburger Allgemeine, though they have an obit for a woman named Helga, born Bednarek in 1935 and dying this year.

As for his pot-war life, a well-researched article in the German newspaper Die Zeit details that Bednarek was imprisoned in the JVA Butzbach, that until 1960 he lived in Schirdingen, had run a restaurant at a train station and later worked as an accountant for a supermarket there. At the time, the article is written, 1974, a petition for clemency for Bednarek was under consideration filed by Helmut Becker and Gerhard Hoffmann, both jurists and professors at the university of Marburg, who were interested in representing prisoners in Butzbach. It also mentions that the appeal for clemency is supported by a variety of former Auschwitz prisoners from Poland, namely Konrad Szeneda, former Catholic prisoner and Catholic minister.

This publication by the Fritz Bauer Institute on the trials of Nazi criminals in Hessen mentions on page 108 that the appeal for clemency was granted and Bednarek was released in 1975.

What happened in between 1975 and 2001 is harder to reconstruct. Apparently someone named Reni Rieger has published a term paper or BA thesis on Bednarek in the GRIN publishing house, which is one of Germany's less reputable publishing mills offering authors to publish their stuff for 50 Euros and the see what they get from the sales. Their principle is just to churn out as much as they can and see what money they can make off of stuff that costs them nothing. Thus I am a bit skeptical as to how useful that'll be for his post-1975 life but I'll keep an eye out for it and see if it is useful if you want, though I'll doubt I can find it since it is not really in any of the libraries I usually use.

This is what I could come up with so far. You might find an obit if you email the Oberpfalzer Nachrichten or the Augsburger Allgemeine Zeitung though there is no guarantee that one was published. Several websites also claim that Bednarek died on February 27, 2001 though that I could not independently verify.