Alright, so I installed OptiFine recently and it messed things up.
I am on Minecraft Version 1.8.9, using Forge. I have the following mods installed:
Realistic Terrain Generation
Aroma's Dimensional World
and of course OptinFine. I downloaded the OptineFine Jar, put it into the mods folder and installed it. I then loaded up my world to find that TA-DA! All of my tools from Tinker's construct were gone, all of my Diamond Chest from Iron Chest were gone, and my tent (which is larger on the inside than it is on the outside, and has a lot of chest inside it as well) is also gone. But hey, at least my texture pack looks better.
I do not have restore points for my saves folder.
So, first question: What the hell did I do wrong, and how can I avoid it next time?
Second question: If I restore Windows 10 to a restore point, will that also get me an older version of my Minecraft save folder?
Upon further exploration of the world, the damage isn't as bad as I had feared. Ever modded item is either gone (Like the tools) or replaced by another item from another mod. My Diamond Chest got replaced with Hopper Ducts, my smeltery was was replaced by an assortment of different items, and my portal to my mining dimension is gone... but I'll replace everything and move on.