MediaWiki supports pictures saved in the PNG format.. after a fashion; thumbnails for PNG files will not generate properly when the original file is bigger then 12,5 megapixel. It is understandable when admins delete a file that is broken. Reasoned but problematic actually even unacceptable for the reasons given below.
Pictures saved in the PNG files can be saved without losses. This means that the quality of a picture will not degrade never mind how often you save it. This allows for the collaborative editing that is so much part of our ethos. Collaborative editing is what makes Wikipedia what it is. The majority of the pictures at Commons have been saved in the JPG format it is only because the pictures are never updated that the quality does not deteriorate.
For people who work on our pictures, lossless formats like TIFF and PNG are preferred. The PNG format is particularly nice because it is well supported on many computer platforms and in many applications. It is an ideal format for people who scan high resolution pictures from print, folders or books.
The best practice for restorations asks us to retain original material and this is irrespective if a scan was done by a GLAM or a Wikimedian like Shoemaker's Holiday. It is utterly frustrating when on the one hand support for the TIFF support is promised while the PNG format that is as deserving fails us because it has only partial support.
Technically the PNG format is in some ways superior to the TIFF format because it requires less storage. The one reason why we need to support the TIFF format is because the chain of provenance is maintained when we retain a copy of the original material from GLAMs. This has proven a powerful argument that helps GLAMs to consider sharing their content with us. At this moment we do not show our TIFF files at all. This is known and accepted and as such, our TIFF files are safe.
People are not as aware about PNG files and files have been deleted without following the appropriate procedures. Informing about the issue is what needs to be done for now. Fixing this bug is the real solution.