The last #1 seed down 3-1 to the #8 seed came back and won the series. That was in 2001 when Detroit came back against T-Mac's Magic. Last year the Phoenix Suns were down 3-1 in the first round and came back. So it still is possible. This is a year of nevers for the Mavs.
Never been the #1 seed before
Never won the Southwest division
Never had a 61+ wins season
Never had a 17-game winning streak
Never had a 14-1 record on back-to-backs
The Mavs have put all these nevers to rest this season. And now the Mavs need to put these nevers to rest.
Never won a playoff series being down 3-1
Never won a NBA Championship