Edited addition to OP:
I downloaded the app called MacroDroid from the Google Play store and set it up to automatically enable wifi once daily if it is disabled. With MacroDroid’s system of Triggers, Actions, and Constraints, this was as simple as setting a Trigger time each day (I chose 5 a.m., because it would not interfere with anything if I had disabled wifi for a reason), selecting the Action to enable wifi, and selecting the Constraint that it would only do so if wifi was disabled (so that the app wouldn’t take any needless actions). It should look something like this screenshot in the app:
There are several other ways to use MacroDroid to remind users to enable wifi after it’s disabled. Continue reading this thread for ideas.
It only recently happened to me for the first time, but others may have experienced the same problem. I turned off wifi on my phone, then I forgot to turn it back on – for several days… In four years, I might’ve used up my cell data during a billing cycle once. Now I’m twelve days into a billing cycle with less than 10% cell data left. I find myself wishing there was a notification that told me, “Hey, your wifi has been turned off for [24/ 36/ 48/ whatever] hours. Did you mean to do that?” So, I put the question to the community: Is there a way to arrange such a notification? App or phone settings would work for me. I’m using a Moto X Pure.