Similar to the boost to attendance you get after promotion, there is a penalty to attendance after relegation. It should last until approximately the allstar break, or slightly after (the end of games against the other conference teams). After that, attendance should pick up to typical D2 levels.
Like other people said, it becomes all the more important to win away games before home games, and win TV and rivalry games. It's possible that a higher level PR guy might help if you currently have a really low one (like 2, 3), but the exact extent of that boost is totally unknown.