I think the key is “ragakkhayo Nibbanam,dosakkhayo Nibbanam,mohakkhayo Nibbanam”.
Nibbana is attained by eliminating greed, hate, and ignorance (of the Four Noble Truths) completely.
When that happens, one would have cultivated ALL sobhana cetasika to the maximum. So, it is not correct to say that any sobhana cetasika (including metta, karuna, etc) would be eliminated.
Sobhana cetasika also include alobha and adosa. amoha comes via the panna (wisdom) cetasika; see, “Cetasika (Mental Factors)“.
What happens is the when panna is optimum, one not only sees the futility of staying in the rebirth process, but one’s sanna and citta will also be automatically adjusted to that.
Then one’s mind will not grasp (upadana) any bhava at the cuti-patisandhi moment.
If I have stated that alobha, adosa, amoha will also be removed at Nibbana, please let me know.