The actual effort required to maintain the code will vary depending on what the code does, the environment the code runs in, and the needs of the code's end users.
Unmaintained code will ultimately fail the same way that all other things that humans build do. If someone does not maintain the code, it will eventually degrade and fail.
Anytime you write code, especially for a long-lasting endeavour, you should consider how the code you write will be maintained and what might cause it to fail sooner than expected.
I also have a maintenance contract for one of these: https://arsandbox.ucdavis.edu/
It turns itself off at night and back on in the morning. 3 years running now without touching it once, used by hundreds of people daily.