What would you do if someone sends you an email inviting you over for a meal, a movie or whatever and you cannot go?
Here's what I would do: thank him for the invitation and then regret my inability to make it.
Some people however choose silence! I really don't mean any offense to them but I cannot understand this. Why would they do that? Why not respond and end the suspense? If you don't do that, the host and all other guests are left wondering what to expect!
We must all really 'close the loop'! End the suspense. Respond.