You may want to take some classes in Notes development, or even pick up a book. Since you are still on Notes 6 (or 7) "Lotus Notes and Domino 6 Programming Bible" by Rocky oliver, Brian Bentz and several other well-known Notes developers is a great pick:
You can solve this problem in several different ways. It is exactly this kind of things Notes is realy good at.
This is how I woudl have solved it:
Create a new database to hold the responses.
Create a survey form (the form where the users select the events they will attend, and reason for not going).
On the save/submit button, you add some code that will take the responses and build a number of new documents, using another form (let's call it "Event Response").
Each event response document will contain the name of the user, the name of the event (perhaps you have an event ID as well?), the response (attending/not attending) and the reason for not attending.
So if there are 5 events on the survey/sign-up form, you create five separate documents.
Thsi way it will be much easier later to generate views/reports of what events specific users attended/declined, etc.
The original survey form does not need to be saved after you save all the values/choices to the event response documents. But you could save it as a history, if you like.
Now when you have this database built, simply mail the survey form to the users. Make sure you used the option "Store form in Document" on the form.
Just make sure your code in the submit button point to the correct database.