You can simply prohibit destroying the neutral unit that was used to escape (if that unit had a valuable stack that wasn't destroyed and disappeared after the escape procedure). That is, it's up to you to decide whether it's more important to escape and reveal the neutral unit, or to lose the hero/city, but then be able to destroy that neutral unit if it guards a strategic location...
Therefore, I believe that Ataman's rules regarding the weakening of troops are reflected more accurately.
It's easy to check - if the player reports in the description that they escaped, indicating where exactly, then you can see these neutral units in the final save, and by performing simple calculations to count the remaining units, you can confirm that everything happened as described... :) But this is such a rare case that I doubt we'll ever see it happen...