In the final chapter of the manga, the first thing Sailor Cosmos says is:
コルドロンに散っていったセーラー戦士たちのセーラークリスタルが もとどおりの姿をとりもどし 自分たちの星へ 還ってゆくのよ
All of the Sailor Guardians' Sailor Crystals, now scattering around the Cauldron, will get back the forms they had before and return home to their own stars.
まだみんなコルドロンから生まれたばかりのスターシードだけど それぞれの星にたどりつくころには成長してもとの姿にもどっているでしょう
For now, everyone is still only a newborn star seed emerging from the Cauldron, but once they each have finally made their way back to their star, they will have grown up and returned to their original form.
She then assuages the Sailor Quartet's fears that Sailor Moon is no more by telling them:
(Original Serialization Text)
あなたたちの プリンセスも みんなと同じようにあのラムダ・パワーで 再生されました
Your princess, along with everyone else, has been reincarnated thanks to Lambda Power.
いまごろはあの光の渦の中 三十世紀へ無事に還りつくことでしょう
By now, this whirlpool of light should have led them safely to the 30th Century.
(Tankoban Text)
安心なさい あなたがたのプリンセスもほかの戦士たちと同じように あのラムダ・パワーで再生されました
Rest assured, your princess, along with all the other guardians, has been reincarnated thanks to Lambda Power.
いずれあの光の流れにのり 三十世紀へ無事に還りつくことでしょう
Eventually, this river of light should lead them safely to the 30th Century.
In other words, Usagi and company do
not return to 20th century Tokyo and their regular lives as I'd always thought; they're sent straight to the 30th Century and arrive there in their recognizable teenage/young adult bodies.
This means that history
has changed: In the BMC arc, King Endymion said Usagi became Neo Queen Serenity when she was 22, which is when she had Chibiusa and stopped aging. Since the manga is set contemporaneously, Usagi, who was 14 in 1992, would have turned 22 in the year 2000. Since Chibiusa is 900, this means the 30th Century we see is the year 2900, and Neo Queen Serenity is 922 years old (78 years shy of the end of her allegedly-but-most-likely-retconned 1000 year lifespan).
But after Eternal Sailor Moon sacrificed her life in her battle against Chaos and melted into the Galaxy Cauldron along with everyone else, it seems that history has been resigned to a different timeline (even though that would seem to complicate Sailor Cosmos's situation even more): Usagi may still become queen at "22", but she will now be "22" in the year 2900 instead of the year 2000. Not only that, but since she has arrived in the 30th Century newly reborn in her familiar form, she is no longer the daughter of Ikuko and Kenji, sister of Shingo. The other Sailors and Mamoru are likewise no longer members of their former families. All of their friends - Naru, Umino, Motoki - are all long dead, never knowing what became of their friends.
This all brings me to my point: If she is no longer Kenji and Ikuko's daughter, is "Usagi" really still "Usagi"? In the same way Princess Serenity is no more, it would appear Usagi is also no more (even if she still uses that name); only Neo Queen Serenity remains.