The problem is Mike if nobody comes forward to get the people who want it, it just doesn't happen.
I think you will find that G&T will want to pack and go when the concert is over.
As for Mrs Sooz, I think you will find that they will probably want to leave after the concert.
The last time I tried to get a singaround after the concert it was a big failure.
However you never know, somebody might come forward and get it going.