At present, there is no way to "solve" a 0-save-req + no exit level, hence why replays are generated inappropriately.
Yes there is - you simply start playing such a level, and bam, you have immediately solved it. By definition, you have solved a level when you have rescued a number of lemmings equal to or greater than the save requirement, which happens immediately at the start of gameplay if the save requirement is zero, regardless of how many exits the level does or does not contain.
The
ONLY possible outcomes here are, as detailed in reply #3:
(a) nothing changes, (b) replays stop getting autosaved on levels with a 0 save requirement (perhaps unless at least one lemming is actually saved), or (c) a special case is introduced where the "save requirement gets capped to number of lemmings that there's exit capacity for" rule doesn't get applied on levels with no exits.
Even these
technically fall outside the acceptable suggestions at this point, but I am choosing to make a special case because (a) there is a very good reason behind it, and (b) both of the options that aren't "do nothing" there are
extremely trivial to implement, as in, it would take less time to make one of those changes than it has taken me to write this post.
The only further discussion I want to see in this topic is about which one of THOSE THREE options is preferred. If you want to talk about hypothetical alternative modes, while you are certianly free to do so, you will need to do so in another topic, outside of the Bugs & Suggestions boards (such as the main NeoLemmix board or the general Lemmings Main) - and understand that it is near-certain that they will remain purely hypothetical.