Logically it would not free up space, since the unit array and the descriptions array are separate from the nation array and the array entries don't actually get deleted, they just get deactivated by the mod. In other words, a mod is just an overlay on the base game, a Halloween costume, if you will, but the plumbing is still the same underneath.
The only viable solutions are for the array sizes being expanded in a patch, but that probably entails the ranges of numbers being adjusted as well. IIRC modded unit range was 2000-5000 or something like that, and the number of units in the game already is 1917, so any more big expansions in patches and the base unit range runs into the mod unit range, causing conflicts.
Things could be somewhat alleviated if it was possible to add descriptions separately into an array and then reference them by #description <nbr>, or if existing descriptions could be referenced by #description
<monster nbr>, which is how the game handles descriptions (references them from a separate file).
I need to set aside a couple of days for mod related issues, make a coherent list of them and send it on...