As an FYI You should consider setting up Source Control, it’s free and would allow you to go back in time and correct issues like this. I know hindsight is 20/20, it’s a lesson we pretty much all learn, but it’ll help you in the future. It’s just a few minutes to set up and adds a lot of benefits.
As for whether it’s hard to create an RPG from scratch… the short answer is yeah, the longer answer is it depends on how complex you want your RPG to be.
An easy way to get started is to click Add Content (I think, it’s a button near the content browser) and add a content pack from one of the templates… third person or top down for example. Then you easily get that stuff back.
Otherwise if starting with animations is where you want to start you can look into Animation Blueprint and research that… the first road you’ll likely hit though is lacking an anim pack for RPGs. I think maybe the couch knights pack will have some, but I’m not sure
But to get the default mannequin anims back just add the content packs, I think the top down kit and third person kit has them.