A lot of music has been lost too. In the 80s and early 90s¹ a lot of bands started out by releasing singles on vinyl either individually or through tiny labels. The media has a reputation for being damaged beyond use if treated badly. Another media, cassettes, has the same issue. Both of which may also have been discarded. I should imagine that this is just a different version of what has always occurred: the most popular things will be remembered and repeated. This has happened in music and poetry as well as stories which were originally only held verbally (see Homer for an example - not Simpson!!!).

I have total faith that the digital photos will be convertible because the formats are widely known so, even if it will cost, there will be conversion services or readers available. I think the bigger problem is the vast amount of photos the current generations are producing as I can imagine that more photos are taken on an average night out than my Mum took on our annual holiday (vacation to you overponders ;-)) which accounted for over half the yearly photos taken. Also loss due to services disappearing. How many people back up their Facebook photos?

As for databases? I think that if there is some real value then the data will have been transferred and if there is some historic value than there will be digital historians who will learn to dissect digital archives. Perhaps akin to archeologists. The rest will be eventually be discarded as irrelevant.

¹ It may have occurred longer than this but I am not that knowledgable. Sorry.