Maybe

Since I'm an English student, I think it is my duty to teach other people how to properly use the English language.

If someone asks you if you're going to do something with them, here is a flow chart to show how your actions will be regarded:



I think that from this, we can see that it's never worth saying 'yes' if there is even the slightest chance that you will not be able to go. This rule applies especially if you know you won't be able to go, but are trying not to hurt people's feelings. Don't do it.

'Maybe', I would argue is worse than 'no', but really it's about the same. Basically, say what you mean when it comes to this type of thing. Otherwise you're a dick, and no one wants a dick to come to their party anyway. The show will go on.