Homer, that doesn't seem to be what God commanded. This is what I found:So what right did God have to command that any prophecy which failed to come true would cost the life of the false prophet?
But the prophet who presumes to speak a word in my name which I have not commanded him to speak, or who speaks in the name of other gods, that same prophet shall die. Deuteronomy 18:20
Jonah's prophecy that Ninevah would be destroyed in 40 days, did not come true. But Jonah didn't qualify to be put to death because God did command him to speak this prophecy.
Consider's Micah's prophecy concerning the destruction of Jerusalem. Micah's entire prophetic message has become one of the books of the Old Testament --- placed into the "inspired canon".
Therefore because of you Zion shall be plowed as a field; Jerusalem shall become a heap of ruins, and the mountain of the house a wooded height. Micah 3:12
Did Michah's prophesy come true? According to the record in Jeremiah, it didn't, because God changed His mind.
The priests and the prophets wanted to put Jeremiah to death because he prophesied destruction upon Jerusalem. Then we read the following account:
Then the officials and all the people said to the priests and the prophets, "This man does not deserve the sentence of death, for he has spoken to us in the name of the LORD our God."
And some of the elders of the land arose and said to all the assembled people, "Micah of Moresheth, who prophesied during the days of King Hezekiah of Judah, said to all the people of Judah: ‘Thus says the LORD of hosts, Zion shall be plowed as a field; Jerusalem shall become a heap of ruins, and the mountain of the house a wooded height.’
Did King Hezekiah of Judah and all Judah actually put him to death? Did he not fear the LORD and entreat the favor of the LORD, and did not the LORD change his mind about the disaster that he had pronounced against them? But we are about to bring great disaster on ourselves!" Jeremiah 26:16-19 NRSV
So a true prophet of God may prophesy things which do not come to pass, not because God didn't tell him to prophesy these things, but because He changed His mind afterward, responding to people when they change their own minds and their ways.
Jeremiah said the same thing in his own defence.
Then Jeremiah spoke to all the officials and all the people, saying, "It is the LORD who sent me to prophesy against this house and this city all the words you have heard. Now therefore amend your ways and your doings, and obey the voice of the LORD your God, and the LORD will change his mind about the disaster that he has pronounced against you. Jeremiah 26:12-13