Hastert's decision stands on its own as the appropriate thing for the vanquished leader taking responsibility for a defeat. Gingrich did the same thing when the Republicans made a poor showing in the 1998 election -- a result largely attributed to the disatisfaction of the electorate with the decision to impeach Clinton. Whatever one may say of Hastert as Speaker and party leader, he has followed the appropriate honorable forms. (Unlike the Dems, who inevitably stick around and hold on to leadership. Terry McCaulif should have stepped down as head of the party in 2002 after losing the Senate.)
The question is whether the Rs will see an exodus similar to that which hit the Ds after they lost both Houses in 1994. After 1994, a number of southern Ds switched parties (which represented a realignment of "Dixiecrats" to Republicans) and a number of long-time Ds simply left.
Although the election seems far off, we are reaching the break point for Congressional incumbents to make a decision if they want to give their party a chance to find a replacement and have a real campaign. And things look bleak for the Republicans at the moment. Dems are energized, Rs are demoralized, and polls show more independents trust the Democratic Party over the Republican Party on most issues. That's a bad time to lose the advantage of a seat held by an incumbent.
Mind you, the Rs can still turn things around before the election. But incumbents need to make a decision over the next few months. Will sitting members, disenchanted with the new Congress and unwilling to risk defeat in an election simply stand down? Or will they stay on to give their party an edge?