At the moment, it seems unlikely that Clegg will actually win power, as most models now predict that Labour will win the most seats despite coming third in the popular vote (due to the geographic distribution of votes in a first-past-the-post system). Such a result would likely produce an unwieldy Labour-LibDem coalition headed by Gordon Brown. This would be a disastrous result both in terms of policy and in terms of public reaction, as Brown will stay in power despite being roundly defeated by both Clegg and David Cameron. However, those predictions are based on "uniform swing" models, which assumes that any changes in vote share are distributed equally across the country (to understand, play with this election seat calculator from the BBC). So, the models could be very far off, especially with the country apparently going through a political realignment. Also, if Clegg continues to win debates, his poll numbers could continue to rise dramatically and sweep him into 10 Downing Street.
Obviously, this seems be a huge blow to the Conservative Party, but before we get too panicked, there may be a small silver lining. Assuming that Cameron loses, Britain will be stuck with either an unstable Brown-led coalition or an unstable Clegg-led coalition (my money is on Clegg) - meaning that Britain could be back at the polls in a snap election before the next term expires. Furthermore, Clegg is likely to live up to his billing as "the British Obama" by driving the country off a left-wing cliff and horrifying voters that failed to read his policies carefully. Under such a scenario (or under an illegitimate Brown coalition), both the LibDems and Labour will lose credibility after governing together, thus sending the electorate into the waiting arms of the Conservatives. Furthermore, as the moderate Cameron would likely resign the party leadership after a humiliating defeat, the Conservatives are likely to be under more conservative leadership by the next election (as Cameron takes a lot of heat for running so far to the center as to blur the lines between parties).