Jumping off the ship would've required courage and heroism. I suppose telling them to throw him over shows a little courage; but deep down he was a coward.
I doubt any of that was the case. When we watch movies of ancient times they tend to show biremes and triremes which were ancient warships so they were built different than merchant ships. Merchant ships would only have a fraction of oars used only if there was no wind. As they were propelled by wind.
Being merchant ships they also had a different purpose and that was to carry goods and passengers. So they had very deep hulls so they could carry things like maximum amounts of grain. So the merchant ship would have carried cargo and passengers below deck. So all of this is going on and the conversation would have been happening below deck. So would not be just as simple as jumping off the ship.
Depending on the sea state of the storm good luck walking up the ladder to topside to climb the rails and then jump off. So anyway it was a merchant ship and Jonah would have been below deck the scripture even points out that is where Jonah was and he was actually asleep during the storm and had to be awaken.
Jonah 1:3 But Jonah rose up to flee unto Tarshish from the presence of the LORD, and went down to Joppa; and he found a ship going to Tarshish: so he paid the fare thereof, and went down into it, to go with them unto Tarshish from the presence of the LORD.
Jonah 1:5-6.............But Jonah was gone down into the sides of the ship; and he lay, and was fast asleep.
6 So the shipmaster came to him, and said unto him, What meanest thou, O sleeper? arise, call upon thy God, if so be that God will think upon us, that we perish not.