-아/어/여라 in the middle of a sentence has one of the extended meanings of the quote form -아/어/여라고. 교실이 떠나가라(고) and 배꼽이 빠져라/빠지라고 are specialized forms indicating the intensity or urgency, or sometimes (a sarcastic) intention, On the surface, they have the command form of -라고, like telling someone to do something, but they actually mean 교실이 떠나가게 할 듯이 / 떠나갈 만큼 and 배꼽이 빠지게 할 듯이 / 빠질 것처럼 . It is an idiomatic way of describing a situation or the feelings of the subject. One clue about this usage is the fact that the object is usually not a person, so that the original meaning of quoting or commanding can't apply. Here are other examples. - 걸음아 날 살려라(고) 뛰었다 = '걸음아 날 살려라'라는 급한 마음으로 뛰었다 = I ran like my life depended on it. - 한 달 동안 죽어라고 일만 했다 = 죽기라도 할 듯이 일만 했다 = I worked myself to death for one month. - 친구는 될 대로 되라고 행동했다 = My friend acted like he didn't care whatever happened.