The Talmud says that Malachi is the last Prophet:
ת״ר משמתו נביאים האחרונים חגי זכריה ומלאכי נסתלקה רוח הקודש מישראל ואף על פי כן היו משתמשין בבת קול
The Sages taught: After the last of the prophets, Haggai, Zechariah, and Malachi, died, the Divine Spirit departed from the Jewish people. But nevertheless, they were utilizing a Divine Voice.
My point is that Malachi cannot be considered the "last prophet" in the absolute sense, since we know that Moshiach will be a prophet too and will come after Malachi.
So my question is: is it conceivable that G-d could send another Prophet after Malachi, before Eliyahu and Moshiach arrive?