When the Beis Hamikdash is restored, sacrifices are supposed to resume. But why? For centuries now we have been taught that the offerings of our lips replace bullocks. For what reason does korbonot need to resume?
G-d neither needs nor wants sacrifices, and only allowed it because people in ancient times felt differently. It is a concession to human needs. The Rambam also states that this is not only his view but is the view of the prophets.
We can add that the ancient rabbis around 70 CE when the temple was destroyed also felt that sacrifices were unnecessary. Therefore when the temple was destroyed, they did not seek a way to continue sacrifices. It would have been easy for them to do so if they felt it was necessary.
Of course, as is to be expected, many rabbis disagreed. We still have many references in the siddur praying for the restoration of sacrifices. But the siddur is a compendium of many often conflicting ideas, which prompt us to think and to remember the past. Abravanel agrees with Maimonides and cites a Midrash.
Additionally Rabbi Kook and the Midrash states that grain will be offered in the Third Temple.