Can a small dermoid ovarian cyst go away on its own?

No. Functional cysts such as follicles are intended to rupture (that's ovulation, ) many abnormal cysts (endometriomas, benign tumors, dermoid cysts) will not go away unless removed. SO if it's a dermoid it will stay and keep growing; conversely if it DOES go away on its own it wasn't dermoid. Good wishes.