Since when did it become antiquated to expect a response when one asks a friend if they'd like to attend something? Oh, wait. Yeah. "Ghosting."
In my world, "ghosting" is actually an IT expression indicating that the computer system is being set up with a uniform desktop via network broadcast. In the wider ergot, however, it means that someone who is disinterested in continuing a friendship or relationship ignores the other individual entirely until they give up and go away.
Look, I have a timeline here. If tickets have to be purchased in advance and you're not interested, the correct response is, "No, I don't want to go," or "I'm really not interested in that," or something along those lines. At some point, if you change your mind or get around to responding, it may just be that I've already had to schedule it when you can't go or it would involve reorganizing my entire schedule around accommodating you.
The thing is, while it's easier to "ghost" or ignore someone, it's also cruel. Just say no, and move on.