I'm not so convinced its so idle. Your take on all fans coming back, is similar to New Years resolutions every yr - while you are correct that many will come back, just like most New Years resolutions ( smoking/weight) last only weeks, there are those who stick to their guns.
I think baseball lost many fans, and last Hockey lockout, a great deal left. I work with two people who flat out refuse to watch any NHL games since the last lockout. I'm sure another lockout will further hurt an already damaged game. Some cities like Toronto, Boston, Philly, etc will always be ok. But others like NJ, TB, Florida, might really see some thin crowds.