(This should have been in my last post nut it was already long enough.)
R’ Herzog emphatically rejects the Ohr Sameach’s pshat. He agrees with your sensibilities (Randomex) that it doesn’t make sense that the murderer can’t leave for pikuach nefesh, but he concludes that it’s a gezeiras hakasuv and ‘???? ??????? ?????? ????????? ?????? ????? ??????? ? (he doesn’t quote the entire pasuk). So according to him Dorothy would not have been able to leave under any circumstances, barring the death of the kohen gadol.