Scripts

The loop will put a load on the map (albeit a small one) constantly. The trigger will spend a noticeable amount of time at the start of the map, but won't put a load on it afterward. The most optimized option is to create a HERO_MUST_SURVIVE task, if, of course, it needs to work from the very beginning. Perhaps, it's possible to organize auto-activation based on conditions using dependencies, but I don't know how.

Regarding the "Invalid creature index" error: it's possible that if a creature is missing in the i-th stack, the GetSavedCombatArmyCreatureInfo function issues a warning. To catch it, you can add a print statement inside the loop after retrieving the information: print(i, "-th iteration passed"), and see what prints are output. If the prints are mixed with the error, then it's just a warning; if one of the 7 prints doesn't appear, then it needs to be fixed.