An immediate reshuffle would be stupid (which is why I think it'll happen). The correct thing to do would be to calm down and take a good look at the actual results (not the bbc poll of wards rubbish). And then
don't try to work out why results in most areas were poor (because that's obvious) but try to work out why results in some areas were especially bad and why results in some areas were better. Better to learn from your mistakes and plan for the future than go into the usual frenzy of panic, denial, exaggeration and scape-goating (all four tend to (and are) happen at once, oddly enough). If the latter happens, the only people who benefit are the media (because you're then playing into to the angle on the elections that they came up with before a single vote was counted) and, of course, the Tories.
But before they do anything like that Labour need to realise one thing. This isn't about turnout, or voters staying home, or 'usual mid-term blips', or 'exceptional economic circumstances'. It's this - voters don't like you.
Voters generally don't like long-serving governments. The thing that a lot of people don't seem to have quite grasped is quite how "normal" all of this is. One reason for that is because it's not actually much of a reassurance to
anyone as it's
also normal for long-serving governments to lose re-election
and for the new government to start doing badly in local elections as soon as it takes power. No one wants to admit that (of course this has all been the case ever since local elections started to attract national media attention).
Hmm... not many. Certainly not enough to be worth factoring into any future considerations. If this were otherwise than maybe the overwhelming majority of the electorate wouldn't have stayed at home. Of course mere unpopularity is bad enough.