Things won't look brilliantly hopeful regardless of who's in charge. Consider:
First, some stats
Labour won in 2005 on about 35.2% of the popular vote (to the Tories 32.3%). That was how close Blair and Howard were. Labour still won, despite a controversial war, because Blair promised not to stand again, the economy was okay, and the opposition still couldn't persuade the electorate to give them a chance.
Now some analysis
At the next election: the economy will not be as good; the opposition are likely to be more palatable to the electorate; and the Labour party is unlikely to get a big boost by its leader promising not to stand next time around.
And finally, a prediction
Conclusion: the Tories will most probably score more of the popular vote than Labour. Will that mean a Tory majority? I don't know, I'm not sufficiently anoraky to know the ins and outs of the constituency breakdown of the national vote. Answers..?