Benefits of distilled water: I myself dont and wont use distilled water as 1 of the key things to making water distilled is the evaporation of O2. I want more O2 in my water not less.
Safe time for water not going on plants: This is a lil harder since you didnt say what kind of system you have so I will guess and say you are doing either a drip or DWC either way you should have plenty of time to empty, rinse and refill rez without any issues unless it takes you a couple days to do so:wtf:
Roots have gone to rez: Again dont know what system but roots are going to grow and they are going to seek out what they need. No different from us, if we get hungry we go to the store and get food. Roots will do the same thing, they will extend looking for what it wants. I use to run a small E&F tray and roots use to always make it down the pipe and find the rez but I never had a problem, just make sure the water doesn't get blocked off.