Or HaChaim on Exodus 9:29/אור החיים על שמות ט׳:כ״ט

1 והברד לא יהיה עוד, "and the hail will cease to be, etc." No new hail will fall, whereas the hail which had descended already will cease to be. Moses' promise was essentially what is described in verse 33, i.e. that the hail and rain stopped in mid-air. According to an aggadah in Berachot 54 the function of that hail which was arrested in mid-air was completed in the days of Joshua when the latter was engaged in the conquest of the land of Canaaan (Joshua 10,11) when hail stones fell on Israel's adversaries.

2למען תדע, "so that you will realise, etc." Moses told Pharaoh that he did not pray for Pharaoh in order that he should release the Israelites from bondage, he did not believe Pharaoh's assurances. The only reason he prayed was so that Pharaoh would acquire greater respect for the power of G'd.