A major conference, and advertising. All on a “can you come”, and a “maybe”? No written communication clearly spelling out what’s expected, with dates, times, accommodations, etc.?
This isn’t a “having a get-together, can you stop by” kind of thing. People’s reputations are damaged, people’s wallets are emptied, and a lot of people end up disappointed. How does that reflect on you? How does that reflect on the conference organizer?
Do you keep in mind the business end of things when putting together, or participating in, a conference? Whether you’re a “big name” or new at the game, you should.