could you perhaps use these pages as a way of capturing visitors email addresses? I.e 'The above event has now sold out/ taken place but to be first to hear about the next event (by the same group/artist) submit your email address here?
I think it is good to have these pages still on your site as it shows visitors you've sold tickets for lots of past events and I suppose if the pages are well optimised it will see you rank for tickets for the particular artist on the page.
Either way I'd keep the pages.
the topsmagic site takes a while to load though