The sport will move on and girls will still run 1:55-1:56 without Semenya (not sure you can run much faster than 1:55 clean IMO)
From 2008-2016 Rudisha was just a dominate as Semenya (prob more so) and most of the sub 1:43 performances came from races with him in it (see below). He hasn't been on the scene the past two seasons and we are still seeing athletes produce fast times, with Korir 1:42.05 and Amos 1:42.15 in separate races last season. I'm pretty confident that 2020 will be won in 1:42 and maybe even 1:41 given there are two days between the semi and final this time.
David Rudisha 1:40.91
Nijel Amos 1:41.73 Rudish 1:40.91
Abubaker Kaki 1:42.23 Rudish 1:42.04
Mohamed Aman 1:42.37
Amel Tuka 1:42.51
Timothy Kitum 1:42.53 Rudish 1:40.91
Pierre-Ambroise Bosse 1:42.53 Rudish 1:42.98
Taoufik Makhloufi 1:42.61 Rudisha 1:42.15
Duane Solomon 1:42.82 Rudisha 1:40.91
Ferguson Cheruiyot 1:42.84 Rudish 1:42.98
Alfred Kipketer 1:42.87
Clayton Murphy 1:42.93 Rudisha 1:42.15
Nick Symmonds 1:42.95 Rudish 1:40.91