Well the sea represented chaotic and destructive forces in the Hebrew thought (indicated in creation narratives, and the flood was seeing the chaos of creation let loose which parallels and comments of the chaos and destruction already flooding the world through humanity’s violence). That there will be ‘no more sea’ is at least in part a promise that when the purposes of creation are fulfilled through Christ, chaos and destruction will be nor more part of creation or afflict humans anymore.
That said, since the lake of fire is the second death, this must include damaging affects of death, there will still be ‘sea’ while they are present affecting people or creation, so only when all are healed and death is completely defeated can the promise of ‘no more sea’ be fulfilled and completed. And I would hold the same to be true of ‘And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away’, as long as there is the effects and hurts of death and sorrow from their effects, then that promise is not completed either. It affirms death will be destroyed, and all it’s effects on everyone, all of humanity of be healed and brought through death, and their ‘will be no more sea’ as promised.