After a one-day delay in leaving the hospital had '96-watchers thinking he might downscale his ambitions, former Vice President Dan Quayle left Indiana University Medical Center today and said the blood clots in his lungs won't affect his decision on whether to run for president. "To the public I would say I'm on the mend . . . after four weeks I'll be back," said Quayle, 47, who spent eight days in the hospital. He's now taking blood thinners and cutting down on green vegetables -- which happen to aggravate the condition -- to keep the problem from recurring. He said the big decision's due shortly after Jan. 1.