Going back to what I said, I've really only been to 2 full city centre weddings, one was mine and honestly I was bet by the time 1.30am came, and I absolutely loathe singalongs etc so I had no desire to organise anything, I think 1.30/2am is late enough and you've been hosting everyone all day. Like I said a few of the die-hards found a place to go literally a 2 minute walk away so there was no issue with that. Don't most weddings end around then anyway?
The only other one I was at was in Smock Alley and you have to be out of there by 11pm - they had organised somewhere to go on to, but I think a lot of folks bailed at the changeover, I know we did. Ended up on the last bus home, happy days. It was a lovely wedding, though.