Your talk needs to be final and complete on the day your are holding it. You do not need to send the final version to us before, however your short session description will be published online before the conference. In order to get readers interested in your session and make them come and see you talk, keep the description short (limited to 2,000 characters) but pack the most important points / questions into it. 

You can resell your ticket and there are usually plenty of thankful takers to be found. You can also make a cancellation (however you will have to pay cancellation fees).
 

As a speaker you will get free accomodation during the conference at a nearby hotel for two nights .