Every broker has different times that a GTC order lasts on their books. But yes, the traditional time was 60 days. Yep, averaging down levels always stay the same. They never change. So if your limit orders expire, yes, I’d suggest putting them back in.
Limit orders take precedence over intraday market orders because they were waiting in line ahead of time. Additionally, it takes out the hesitation or second-guessing that people do around averaging down levels. It also causes one to stick with the system. And, they don’t even have to watch it or react to it. It also enables one to take advantage of quick spikes down, that many people wouldn’t be able to see or react to in time.