I never did field testing but have worked for eNodeB RRC and S1-AP layers. RRM module at the eNodeB will take decision on releasing the unnecessary established bearer under the radio congestion control. That's why, 3GPP has provided E-RAB RELEASE INDICATION message over the S1-AP.
When an eNodeB releases a dedicated bearer for an UE, it completes its RRC signaling. I meant to say exchange of RRC connection reconfiguration and RRC connection re-configuration complete between UE and eNodeB. Once it is done, eNodeB sends indication to MME by mean of E-RAB RELEASE INDICATION message.