It wouldn't have made as much of a difference as some think. Warren's base would've split between Biden and Bernie. A lot of them were very bitter towards the Sanders camp - at least the ones who still supported Warren by Super Tuesday.
Without an endorsement, absolutely, but Buttigieg's and Klobuchar's only broke so hard for Biden because of their endorsements and an overwhelmingly positive news cycle for Biden, among other factors (the latter also shifted non-Klobuchar/Buttigieg voters to Biden's camp).
If the withdrawal from the race was at least non-hostile and led to a tranche of fresh Sanders endorsements, that could trigger a positive news cycle for Sanders, shifting some floating voters both inside and outside the Warren camp. There were Bloomberg to Sanders to Biden voters out there, and I find it hard to imagine that they were inevitably going to be Biden voters given how far and often they drifted.