This sounds like the question centers on issues of application design and having some sort of understanding of the user.

Regarding the conditions and information that the app needs in order to do its work for the user, you need to know by design what things are provided directly and explicitly by the user (command-line args, form parameters, dialog responses, maybe the contents of data files), and what things are determined by the OS/environment/config/etc (stuff that may be outside the user's control or awareness, including the contents of some data files). It can be easier to make the user understand the problem if they caused it and you can make that clear to them; if the problem stems from something other than their direct input, it might be harder to explain, but you should still try.

As for tying up any "internal" loose ends before exiting a script "properly" in case of a problem, this really depends on what the app is doing. If you intend to keep running (e.g. retry by taking the user back to a point just before a bad input), you need to know what steps, if any, need to be undone, what inputs need to be rewound, and so on. It's a difficult issue to discuss in general terms.

In any case, there's a good chance that users will find ways to break your code that you never thought of. Go ahead and give them some code to run anyway. Make some mistakes just like we all do, and if any particular problems vex you, come back with those.

UPDATE: In response to this part of your question:

Is it "safe" or "good practice" not to die? Or is there some intrinsic value of die that I am missing by not using it?

The intrinsic value of "die" is to acknowledge that for certain conditions, further execution is useless and futile. That's the point of using "die". This can be "contextualized" within an eval block, so that you can trap a bad condition without actually halting execution of the whole script -- that is, by putting a "die" condition inside an eval block, you're saying "further execution within this block is pointless" (but on exiting the block, the main script can still decide what needs to be done next).

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