For all you know, they've blocked every profile that was invited to the party. Why? Who knows? Maybe they don't want people contacting them before the party. We've had this happen a couple of times...a couple reaches out to us a few days before the party and says they look forward to meeting us. Seems innocent enough and we always reply with a generic "looking forward to meeting you, too."...or something to that effect. Then at the party, we might not find them attractive or interesting, but they seem to be of the opinion that we should be obligated to focus our attention on them simply because they messaged us ahead of time. I guess blocking all invitees to the party would put a stop to that, but it's only happened like 2 or 3 times so I don't sweat it. But if it became a regular thing, I'd definitely consider doing it.
Also, who's to say they even showed up to the party? In my own experience going to parties, I'd say maybe 20-25% of the people who accept the invite actually show up. If they blocked you because they recognized you then they almost certainly didn't show up. So if they didn't go, then you basically just cut off your nose to spite your face.
Lastly, if they blocked you then you have no earthly idea who they are or what they look like and chances are they haven't committed you to memory either. You could meet each other at the party and neither of you would have a clue....unless you hit it off and exchanged SLS handles.
In short, don't sweat it. Life is too short to allow people you don't even know to dictate whether or not you're going to have a good time.
T