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Are we totally ready for the so called "DEDOLLARISATION" ?
Who are you referring to as "we"? Different countries have different situations and preparations so it will depend on who you're asking.
Will there be any negative impact on the world economy if a hatch decision is being taken towards abandoning the USD for any alternative?
Birth pains during transition periods are usually present so that's one thing. The more severe impact of this is that US launching military wars against those who would cut ties to their beloved dollars. I can't really tell what exactly they will do but everyone probably knows what they're capable of when they're "threatened".