Okay so I'm so close to finally finishing my world, I can taste it.
I have 117 lots, my DDCache is 0.99 GB. I've also moved all mods that don't have anything to do with CAW onto my desktop and disabled all CAS under CCMagic.
Lastly, I did test in a new blank world, and EIG did save.
So now I'm at a loss of what do to. I'd rather not restart and rebuild, but I will if it's the last resort.
Will your most recent backup save now in EIG? If so, what have you done since then? Can you rework from there? Use lots of save as saves if you find one that still works to have extra backups. Sometimes it might be something as one lot it does not like. I have had to move lots to the library/bin whatever it is called and save again and that has worked at times. And sometimes I can put the same lot right back in and it works. CAW can drive as nuts at times.
So I tried checking a new sims folder and the recent backup. Neither of which worked, that being said I think like @daisylee said there is a lot somewhere that it doesn't like. The farthest save I could go, a save error popped up. But there have been so many different saves. New save as, and new sims 3 folders over the years. Where I've brute-forced a save, because of the save error popping up. That now my entire world is sort of corrupt. :/
I mean, fortunately, I have one of the more recent reiterations in-game. So I can just save my lots and place them back in. Any with the save error, I'll rework. I think I'll also fresh start with a new sims folder. Than only transfer needed mods, cc, and my latest in-game world. @volvenom I also definitely keep your strategy in mind as I get closer to the finish.
Thank you both for your help!