What should you do if you lose the track?

I walked from Blackheath to blue gum forest, and at Beauchamp Falls there had been a landslide (quite a few years ago I think) which had totally covered the track.
I knew the track basically followed the creek down, but I didn't really want to just start following the creek in the hope that I saw the track later on and potentially get myself more lost.
In the end it wasn't a big deal, I dumped my pack and wandered around for a bit before I found it, then went back and got my gear. But it did make me wonder what the best thing to do is if you get lost. Keep moving? Try and backtrack?
What do you do if you're on a schedule you won't be able to make?
I was finishing my walk on Friday, which was forecast to reach 33deg by late arvo in the Blue Mountains, but in fact hit 44 deg by min morning! I managed to keep to my schedule and get back on time, but again it made me wonder. It was a *&%$#! hard slog getting up out of the valley in that heat and I was very tempted to wait out the heat and stay another day. But I had lodged my trip intention and didn't want my wife to get freaked out when I didn't come home that night. So how do you get around this? Should you
Running out of water - to drink untreated or not?
I ran into a couple of German backpackers who had taken 5L of water for 3 days between them and had no purification

They told me they realised they were going to be short (especially given the unexpected heat and the fact they had their ENTIRE luggage for their 6 month holiday with them - 30kg each!!!), and asked if i thought they were better off drinking the water untreated, or just rationing. I didn't know what to tell them. What would you do?
I guess if I was them I would probably have broken the fire ban and boiled water? I dunno.
There were a few other questions I had which I was going to try and remember to post here, but they've slipped my mind! If I remember I'll post again.
Cheers in advance!