The short piece that broke off WAS your antenna. At least the active part on that lead. Having it break could possibly have de-tuned the entire Rx to the point of losing control. It's hard to tell as antenna theory has made such strides, it's hard to predict what exactly happened without knowing exactly how the manufacturer intended it's use. The little circuit board I'll 'guess' is an amp or filter or both. Indicating that particular antenna was the one that captured the weakest of signals from the Tx. Lose it and you've lost most your range and your link.
The antenna less Rx does have an antenna. It's simply printed on the inside of the case. You can see it if you look close.