Here's the precise use of while and repeat until loops (same as while and "do while" loops in C or C++):
While loops check a condition FIRST, then execute code if the condition is met.
Repeat/Until loops execute code at least once, THEN check the condition.
So....in the case where you want to "wait" until a creature is killed, the appropriate use would be:
repeat
finditem !target
until #findCnt = 0
This is because you want to execute the code THEN check the result. Like has been mentioned before, with the while loop, you have to "seed" the value by adding an extra finditem immediately before the while loop (thereby losing any line-saving advantage)
As for the brackets, it is proper coding format to use brackets for anything that is multi-line. Repeat/Until loops have implicit brackets, however, when NESTING repeat/until loops with no brackets, you can have undesired results (if you are an idiot and don't know how to use them, LOL)!!!!