Dumping Lapid would leave him with 20 or so seats, more than enough to enter Bibi's block in good stead, but having to accept the rest of Bibi's current partners. The alternative is, he's counting on thin air if he gets his shot in a month.
from the wiki-wacky page on Yair Lapid:
Election Leader Votes % Seats +/ Status 2013 Yair Lapid 543,458 (#2) 14.33 19 / 120 Coalition government 2015 Yair Lapid 371,602 (#4) 8.81 11 / 1208 Opposition April 2019 Yair Lapid 1,125,667 (#2)
(as part of Blue and White)26.13 15 / 1204 Snap election September 2019 Yair Lapid TBD (as part of Blue and White) TBD 13 / 1202 TBD