I spoke to someone at SeeTickets this afternoon. If you're expecting tickets in the post but they don't arrive in time, they ask that you call them to let them know on Thursday, so they can prepare them for you to collect at the event (like the international orders). I'm sure they can still reissue them without being informed beforehand, but it might take a little longer.
When you call, you could ask exactly what you need to collect tickets (ID, emails, whatever), what to do if you're not the card holder, etc, so no nasty surprises on the day. I don't think mine are going to get here in time now (still haven't been posted, and I leave on Thursday) so I'll probably need to do this too.