Should the other candidates stay in if they can stop Kerry?

First,
Exluding the Super Delegates, this is (according to CNN) the totals for the delegates elected in the 11 primaries and caucuses held so far.

total elected: 540
John Kerry 315 (58.3%)
John Edwards 90
Howard Dean 76
Wes Clark 50
Al Sharpton 9

Ok, Kucinich and Sharpton will almost certainly stay in till the end.  Who cares? Kucinich might not get a single elected delegate and Sharpton won't get more than 100 out of the 4,400 or so total.

Edwards, Dean and Clark have basically said that Wisconsin is the end game.  But, what if the result is somewhere in the middle?  Kerry wins, but gets well under 50% and the 3 other 'serious' candidates all get over 15% and get allocated delegates.  Therefore, Kerry would get much less than half the delegates.  Say a result like:

Kerry 30%
Dean 27%
Edwards 20%
Clark 18%
other 5%

It would show a loss of momentum for Kerry, and suggest that doubts are being raised about him.  On the other hand, the result would also show that nobody else would be likely able to win outright.

The question I'm asking, therefore, is:

If the other candidates can't win themselves, but could possibly deny Kerry the nomination outright on the first ballot, should they stay in the race?