ClearAll[NextHighestIntFromDigits]
NextHighestIntFromDigits[n_Integer?NonNegative]:=Module[{digs},
 digs=IntegerDigits[n];
 digs=FromDigits/@Permutations[digs];
 digs=Select[digs,GreaterEqualThan[n]];
 If[Length[digs]==1,First[digs],RankedMin[digs,2]]
]
NextHighestIntFromDigits/@{0,9,12,21,12453,738440,45072010,95322020}