None of that matters if,
1. Trump didn't undermind the standing of the US in the world
2. If Trump refuses to meet with Kim unless he commits to denuclearization as has been the long standing policy.
If this meeting doesn't affirm 2 nothing else matters and were likely on the path towards war. We already have Republicans asking dems to support giving Trump that authority.
China and Russia have been cozy with NK.
EDIT: Everything you mentioned was set in motion by Trump saying he was willing to meet with Un. Let's not rewrite history for our own narrative.
Trump def sped up the process and is an important player in all this but Kim completing his nuclear program, him going the diplomatic route and Moon embracing Kim’s diplomatic overtures changed the game imho. Moon in particular already said he was open and willing to meet Kim back in 2017, even during the maximum pressure days.
The Pyeonchang Olympics continued the shift when Moon and Kim Yo Jong met in Seoul. Even Abe, who is no fan of the Kim dynasty, briefly met with the North Koreans during the opening ceremony, despite Pence not acknowledging the North Korean delegation back then.
With Kim’s nuke program seemingly complete and him shifting his stance, meetings with Xi, Moon, and the Russians would’ve happened regardless. Trump could’ve declined meeting with Kim for the time being, but things were already in motion prior to Trump agreeing to a meeting. Maximum pressure wouldn’t have lasted long imho.