Personal memories can be made in innumerable ways. The absence of tickets doesn't mean memories, or physical representations of memories, are going away.
As for academic interest, I have to imagine there's a digital repository of playbills or the information therein somewhere that's easily searchable. After all, these types of resources exist for other performances like pro wrestling and mixed martial arts in the form of cagematch & sherdog. I may not have my ticket stub from my first match, but I can still look it up by venue, year and the matches I remember. I can find contemporary news reports and reviews. This can be supplemented with web forum discussions and other social media, blogs, etc. people crave this type of discussion, documentation and artifacts that prove their fandom. I don't think they care about the medium.