The ability had already triggered, so what happens to that noncreature spell now is irrelevant
Multicolor Barrowin and Tomb of Annihilation go hand-and-hand
The same is true if a creature is removed from play while a bestow spell is on the stack targeting it

Release date: 2022-01-22 Chishiro, the Shattered Blade Kotori, Pilot Prodigy Kaima, the Fractured Calm Shorikai, Genesis Engine Aerial Surveyor Drumbellower Ironsoul Enforcer Organic Extinction Release to Memory Swift Reconfiguration Access Denied Cyberdrive Awakener Imposter Mech Kappa Cannoneer Katsumasa, the Animator Research Thief Universal Surveillance Akki Battle Squad Collision of Realms Kami of Celebration Komainu Battle Armor Smoke Spirits' Aid Unquenchable Fury Ascendant Acolyte Concord with the Kami Kosei, Penitent Warlord One with the Kami Rampant Rejuvenator Silkguard Tanuki Transplanter Myojin of Blooming Dawn Yoshimaru, Ever Faithful Myojin of Cryptic Dreams Myojin of Grim Betrayal Ruthless Technomancer Myojin of Roaring Blades Go-Shintai of Life's Origin Myojin of Towering Might Aerial Surveyor Drumbellower Ironsoul Enforcer Myojin of Blooming Dawn Organic Extinction Release to Memory Swift Reconfiguration Yoshimaru, Ever Faithful Access Denied Cyberdrive Awakener Imposter Mech Kappa Cannoneer Katsumasa, the Animator Myojin of Cryptic Dreams Research Thief Universal Surveillance Myojin of Grim Betrayal Ruthless Technomancer Akki Battle Squad Collision of Realms Kami of Celebration Komainu Battle Armor Myojin of Roaring Blades Smoke Spirits' Aid Unquenchable Fury Ascendant Acolyte Concord with the Kami Go-Shintai of Life's Origin Kosei, Penitent Warlord Myojin of Towering Might One with the Kami Rampant Rejuvenator Silkguard Tanuki Transplanter

I get the idea is to build out your deck over time and these are the easiest place to start, but these cards are too important to leave out