2 official rulings from Bandai, last ruled Mar 28, 2024. Straight answers to how this card actually resolves.

If I use this card's <On Deletion> effect to return this card to the hand, does it mean that this card isn't sent to the trash?
No, an <On Deletion> effect activates after the card is moved to the trash. Therefore, the card is first sent to the trash.
Ruled Mar 28, 2024
There are "Sukamon" A and "Sukamon" B in the Battle Area, both of which have this card as their digivolution card. When "Sukamon" A was about to be deleted, it tried to delete "Sukamon" B with this card's inherited effect. On the other hand, when "Sukamon" B is about to be deleted, it tried to delete "Sukamon" A with this card's inherited effect. In this case, can "Sukamon" A activate this card's inherited effect again?
No, it cannot be activated. Until the first occurrence of the first process is resolved, all immediate/interruptive effects can be activated only once each. In this situation, until the first Sukamon A deletion resolves, each of the "When X would" effects can only be activated once, so Sukamon A that has already been activated cannot be activated again.
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