bitcoin is maintained by core developers, would Bitcoin die a natural death if the developers no longer exist? Or if they stop maintaining/developing/upgrading the system?
I bitcoin ever dies, and I don't think it will, it won't definitely be from that cause. Bitcoin is open source, you can see the code on GitHub, and there are many devs working on it. If I'm not mistaken bitcoin is developed though Bitcoin Improvement Proposals (BIPs). These proposals are public and need to be approved. This is how bitcoin gets developed, so there are many devs behind it, and they can't all die.