I have been having trouble with my wold saves. whenever I open worlds in forge, then try to reopen them in vanilla Minecraft they don't show up. I assume it has to do with a current mod having too much content to be removed, as the wold only disappears once the mod is gone. I am just wondering if there is any fix for this, or if it is a consistent problem for anybody else.

You cannot reliably use Forge worlds in vanilla, Forge changes a lot of stuff in regards to Block IDs and their role in the save format. With Forge, vanilla Block IDs are no longer constant.

... They should be unless some mod goes in and screws with the internals of our registries, which has been known to happen.

If using JUST forge, then your worlds should stay compatible with vanilla.

Once you add mod items/blocks tho, you're probably screwed.