Definitely the saddest cancellation I've known. It was a fantastic series in its prime about to reach mainstream popularity, I'll always remember it for that and once Shiro Usazaki has processed all of this and decides her path I hope to see her artwork on the cover of Jump again.
It's likely now that Mitama Security, Act-Age (still so strange to type this), Bone Collection, and Time Paradox Ghostwriter will all end this round since there probably isn't enough time to retroactively continue publishing manga when the final chapters have been written/drawn. Assuming we'll go back to 19 series, by #42 the magazine will look like:
Established (7/19):
- One Piece
- My Hero Academia
- Jujutsu Kaisen
- Dr. STONE
- Black Clover
- Chainsaw Man (Likely ending 2021)
- We Never Learn (Ending 2020)
Safe/Rising (9/19):
'Unsafe' (12/19):
- Mission: Yozakura Family
- Moriking
- Agravity Boys
Newcomers (19/19):
- Ayakashi Triangle
- Magu-chan: God of Destruction
- Hard-boiled Cop and Dolphin
- Me & Roboco
- Honomieru Boy
- Kokousei Kazoku
- Bokura wa Ketsumei
Basically everything below Undead Unluck is free, and with We Never Learn ending in 2020 and Chainsaw Man likely to end in the first half of 2021 at the rate it's going, that would leave an insane 12 spots in the magazine, and if you want to exclude the bottom five that's still 7 'Safe/Rising' series.
Either this will be the best or worst time for new manga to get serialised. I remember there being times when there was maybe 2 spots left for grabs in the magazine, so this is wild. 2020 will likely already have the most new series in a year and if anything doesn't stick early on I imagine they'll just keep on adding more until hits start to appear.