Bad project will also get bankrupt, but the good one knows death is possible so they will prepare for this.
Developers are not only consist with only one person, they are a group and every group has different function, so they will have to work based on their function, when one is gone, one member will step up to the position so the business will continue.
That's why choose a project that are already successful if you are afraid of this kind of risk, with successful project, they have great potential and thy are already making the project profitable, so it's hard for them to leave that money compared to those who are not popular yet.
How many of the altcoins are fully working in a decentralized way that the source code will be opened and subject to further development externally, most of the project that we see has restricted their project to internal development alone and there is no room for external development like bitcoin did.
If a developer and creator of most of these altcoins die, first, the team will stop responding because there is no longer going to be team, as they all will gradually part way, and the moment the team start becoming less active, it would definitely send a wrong signal to he investors who will also withdraw their hands of investment in the coin, and then you see the coin gradually dyeing off the market. Until most of these projects fully embrace decentralization before we can beat our chest for them on continuity.