we don't send ourselves to hell

[Neo-Scholastic]

An omniscient being (like God) can only know that which it is possible to know. The not yet made choices of free agents exist only in potential and not in actuality. It is not possible to have actual knowledge of something that does not yet exist. Therefore an omniscient being cannot know beforehand the actual choice a moral agent will make out of the infinite number of potential choices the moral agent could take.

So prophecies that are at all dependent on human actions are just guesses?

Revelation is just a guess?

OT prophecies have always been contingent on human actions, as in either repent or this (plague, foreign invasion, etc) will happen. The people of Nineveh repented and avoided a dire fate. God can know the potentials and as events draw near can make near certain predictions (as in the case of Peter's thrice denial). As for Revelation you will notice that almost all the action is taken by the Lord.