The same thing happened to my watch last week after 2.5 years the face just popped off. I placed it on my bedside table and came back to it later thinking maybe the glue just gave out not good but possible easy fix.
When I went to fix it, It was dead so I put it on charge to make sure everything was ok with its operation. When I went to check on it,It had started to over heat and for the first time ever was displaying the red thermometer and it was so hot I could not pick it up. So my conculsion was that this is what had happened and caused the screen to pop off.
With a little research I found out that there has been an issue with the Generation 1 Apple Watch sports edition batteries and the warranty was extended to 3 years from date of purchase. I booked into the genus bar to have my watch looked at and was informed that because the battery has not swollen it would not be covered. There is obviously and issue with these batteries and swollen or not this has no broken my watch. Cost of repair quoted at $300 AUD and new generation 1 watch is currently $399 AUD.
The problem I have now is it is not just a battery replacement because when it popped off it broke the touch sensitivity band that is in the seal. (You may have the same problem)
I must add the battery had not shown any signs of age related problems like not holding charge or getting hot during operation.
I am not happy with Apples response I was seen by a part time uni student and I'm close to the 3 year period. So to say I was not pleased with her response of the glue must of just worn out was not the response I was looking for I have several apple products and have never had an issue with any of these products and my watch has been very well looked after.
