I am not going to judge who is worthy of Jannah, individually Allah will decide their fate.
Islam is about individuals, who must act appropriately, as evidenced by Dr Saab’s post, but more than this, it is about society; how mankind must act. If I were living alone then the only thing that matters is survival, where my next meal comes from, but the majority live in communities that need regulating; who does what, how, when and where. The Quran does not mention any Messengers before Noah, so I say that there were none, but there were human beings. They lived without Divine guidance until something changed, quite possibly the development of large groupings, towns and cities, which needed laws to live by. This means that collectively we must act according to Divine Guidance in order to progress upwards, to evolve; stagnation or regression results from backward thinking and wrong acts and this is not an option for the survival of mankind, they must become 'the best of peoples'.
Many a religious leader has said that ‘there are many roads to God’ but a Brahman will never become a Christian even though he says they can reach God through this way! There are, indeed, many roads, manmade religions have seen to this, but only one to Allah Who has completed and perfected our Deen; He has made it necessary for us to follow His way of life and no other and this is done for our collective good.
Individuals need not believe in the Quranic System, but they must not oppose it; the leaders of mankind must implement it and rule over them according to its teachings in order for it to benefit the individual as well as mankind.