I have great news, folks. Better than expected, in fact.
I doubled my phone inquiry with a message on Twitter to House of Ho. They have just responded with the following:
"The plaque is safe & well and will be put back when we have repainted. Come and see the original wall that we have preserved!"They then sent me this picture of Bobby Chinn, who runs House of Ho, with the owner of the plaque, Bob Mandry (whom some of you will recognise from events such as Shadowmania). They are sitting in front of the original wall! I never knew anything of the 2i's remained in tact (apart from a few supporting walls), let alone anything like this. How wonderful that we can see a piece of history.

Now, when I'm next in London, I won't be going to Old Compton Street to see the plaque, but to see the wall. It's the best news I've heard since Luis Suarez extended his contract at Liverpool FC!
J