Yes the auto hover in the 139 is very good. GPS held and often well within the 1-2m.
S&R,
If you are working to a high TDPe of say 300ft in poor weather and vis then I think first you have to ask the question 'do we really need to do this'? If the answer is yes as it can be in the SAR theatre then you have two options if you have an engine failure prior to TDP when doing a vertical procedure. You either keep the helicopter coupled in hov and fly the collective in the descent back to the pad or continue with the OEI profile post TDP.