The best thing you could have done is start walking in the direction that it left with the controller still on. You may have re-acquired connection ,even if it crashed and was still transmitting. You can use the ST10 as a locator by following the green arrow. The arrow is pointing to where you are at in relation to the bird. If the arrow is pointing left, turn to the right some and start walking. This is how I found mine after a tree landing. I was LOS, but looking at the screen when I lost connection.
A couple people have reported that they went looking for theirs after they lost sight of it, only to return to where they were flying, and their Q was sitting on the ground pretty close to where it took off from waiting for them - built in RTH if connection is lost with the transmitter.
Possible that you had some massive RF interference that cause the lost connection, way too strong high altitude winds that it could not cope with, or worst case, GPS signal failure on the Q500, in which case, it has no clue where it is at, and who knows what it start's thinking other than sheer panic.
I do hope you had an SD card in the ST10 controller. Yuneec will want to see that to try to figure out what went wrong, and may be able to help you out.