What became of the Rsvp?

Putting on a good party or other fun event is a lot of work if done correctly.  You want the venue to be perfect, the guest list to be conducive to an enjoyable and convivial time, the food to be delicious and plentiful as well as meeting the dietary needs of all of your guests, and entertainment in whatever form appropriate whether it is music, a baby shower game or even a craft.

You make your plans and send out the invitations, whether by phone, mail, email, in person, or on social media.  And then you wait.  Three days before the event one or two people say they are coming but the other 30 or 200 say maybe or don't reply at all.  What do you do?

At one time I would prepare for what I hoped was a good estimate of guests and sit back and hope it all worked out.  

When did the RSVP stop being "normal"?

Definition of RSVP:  An abbreviation often included in invitations to request that the invitee let the host know if he or she will be attending. From the French term, "Répondez si'l vous plaît," which means "please reply."  http://www.businessdictionary.com/definition/RSVP.html

Miss Manners is my guru and she "considers it an unfortunate concession that hosts even need to state that they would like a response (in sensible times, guests could figure that out for themselves), and finds it distasteful that they feel they must provide the response themselves, in the form of prestamped cards or a voice-mail drop. Especially since such techniques don't work. People who are not polite enough to answer invitations are still not going to answer, even if you lie down in front of them and beg them to kick you once for yes and twice for no."  (Judith Martin, Miss Manners' Guide to Domestic Tranquility, Chapter 7: Entertaining: The Social Contract, p.218)

LOL.

I just don't know the answer.  But now just cancel the event rather than just making myself crazy.