What do backups do?

So my smp server recently crashed after 2 or 3 months of playing in it with my friends because i built too many farms. My friend told me ''you shouldve backed up your server''. So lets say that i backed up my server before killing the dragon and after like a month i killed the dragon but my smp ran out of ram. if i played on that backup server, then would i still get the same achievements i made like beating the dragon? or will i be back to the time where i havent killed the dragon yet