Great question. I will attempt to answer this question from a Jeffersonian point of view.

Jefferson, himself a slave-owner his entire life, actually was opposed to slavery even before penning (quilling?) the Declaration of Independence - he was a paradox of morality and actions. In 1774 he wrote A Summary View of the Rights of British America, in which he attributed blame of extending the slave trade to the Americas onto King George III. This became relevant again two years later when writing the Declaration, as he attempted to include in the many grievances the fact that King George waged " 'cruel war against human nature itself' by establishing slavery in North America (American Sphinx, Joseph Ellis, p. 60). This was clever to do, as a slave owner himself, because it does nothing to attack his own morality, but only that of the King. However, Congress would not have that and deleted the passage from the final Declaration. Why did they delete it? Simply put, it may have angered or separated the southern states whose economic system wholly relied on slavery. So, based upon your question, you have it partially correct that the main reasons were "greed" from the southern states (or fear, at least, that the fear existed) and "losing support for the revolution" by the same reason: southern support.

Now, in answering your third point: Did they think slavery would end by itself? I have seen better answers published on this subreddit before, so I will not try to make and defend a point here. Relevant Post (u/Georgy_K_Zhukov) However, the book I am using to answer your question, American Sphinx by Joseph Ellis, does touch on the fears of Jefferson and Madison. They opposed the Missouri Compromise of 1820's restriction on the expansion of slavery into future, northern states. For both these Presidents, the fear came from both the potential ending slavery as time wore on and the consolidation of government powers and the expansion of the Federal Government (Ellis, p. 329). To speak for Jefferson (and Madison), there was a burgeoning or existent fear that slavery would end by itself later on but not during the time of the Founders and Framers. However, Jefferson also believed after 1820 that "whatever opportunity might have once existed to end slavery gradually and peacefully had itself ended" (Ellis, p. 320), which tells us that the end of slavery (peacefully) had not been guaranteed to occur in the era of the Framing. So, no there was no unanimous agreement that it would end by itself.

As a summary, I'll say that the neglect to end slavery was intentional to keep the southern economy viable and secure support for the revolution within southern states. To the question of, "did they think it would end by itself": There was no such unanimous belief or certainty at the time.

Hope this helps, I will try to answer any follow-ups as best I can.