In Shemos 10:25, Moshe told that Paroh himself will give offerings to Hashem. Did this really happen?
Yes, this did happen.
Verse 12:31 states:
So he called for Moses and Aaron at night, and he said, "Get up and get out from among my people, both you, as well as the children of Israel, and go, worship the Lord as you have spoken.
Rashi says on this:
and go, worship the Lord as you have spoken: Everything is as you said, not as I said. “Neither will I let Israel out” (Exod. 5:2) is nullified. “Who and who are going?” (Exod. 10:8) is nullified. “But your flocks and your cattle shall be left” (Exod. 10:24) is nullified. [Instead,] take also your flocks and also your cattle. What is [the meaning of] “as you have spoken” ? You too shall give into our hands sacrifices and burnt offerings (Exod. 10:25). — [from Mechilta]