Could you tell me what happens if ewings sarcoma is not caught early?

It depends: Depends on what you mean by early. Ewing's sarcoma is usually discovered once it causes symptoms like a mass or pain. It is almost impossible to catch it before then. If it is caught before it spreads, chances of cure are about 70%. If it already spread, the chances go down to about 30% or less. Each case is different though.

Early is hard....: Quantify. Implied in your question is a linear progression from localized to metastatic disease, but this may not be the case. There is research to suggest metastatic tumors are endowed with this ability from the start (the metastatic toolbox). Likewise, even apparently localized disease will shed tumor cells but not form metastases. Suggests different biology. Survival 75% (local) vs. <20% (mets).