Hundreds of thousands of domains were here yesterday but gone today.. either due to lose interest or the person died and no one knew how to keep it going or even cared.
It is very likely that the major websites, such as Chase or Home Depot or Lowes or any of these types of business websites will be here to stay for as long as we do banking and use the Internet.
There are some things that can be done for continuity, such as funding a bank account that is specifically linked to domains and then you'd just have to account for hosting and the domain. If you leave it in your Will, you could keep that bank account going if you don't have greedy family members. In this case, you can set your domain to auto-renew and set autopay for hosting and just make sure you account for the amount you might want to keep it going though this could get expensive.
But unless there is a successor or someone who really is as passionate and cares about your project enough to keep it going, it is very unlikely that it will go on without you.
Software written in a compiled language distributed as an executable for MS-DOS or Windows 95/98/2000 are likely your best bet. Avoid .NET, and stick to either the MS-DOS documented API, or Win32 API. There are likely to be emulators for that running forever.
C Source code from even 2 decades ago is almost impossible to compile correctly, I learned that with my adventure with Stoic. Python from a decade ago doesn't work now either... I learned that with WikidPad. Too many upgrade obligations are built in to source code for them to work reliably in the future, unless you bring along the entire support tree from that time with them.
- Natural disasters can cause it to fall
- Accidents can damage it
- New regulations can prevent it from being used
- Your government could decide to simply close it
Maintaining any service for 100+ years requires humans to maintain it.
then there's
A successful religion (I consider them software running on human hardware)