I use Gecko G210 drivers. These drivers have a disable terminal. When the safety relay cuts it also cuts the control power to miniature relay placed on the same board as the stepper drivers.
When this miniature relay looses power it will give all G210's disable signal (ground disable terminal).
This is in another schematic that i have at school. I could post it on Wednesday.
Really i would have preferred that the drivers had an enable signal instead of a disable signal, but the relay is placed as close to the drivers as possible, with direct wiring.
The drivers are disabled to stop all movement immediately, then they loose 48VDC power.
Stepper safety function #1: Disable all drivers to stop movement.
Stepper "safety function" #2: Cut incoming power to PSU.
Avoid lost steps function": Disable Mach3
NOTE: If the situation is sever enought to need to ESTOP why are you worried about loosing position??(;-)
During an ESTOP this is no worry. The case is that the limit switches are also wired to the safety relay. If a limit switch is triggered and not manually overridden the relay cuts out just like an ESTOP.
The reason for limit switch cut off is not for "human protection" but rather "machine protection".
To meet that qualification you would need to open the incoming power supply and then SHUNT across the PSU to effectively drain down the caps to stop the machine dead in its tracks.
It is clearly stated in G210 manual that the drives will suffer damage if power is cut on DC side of PSU ("fast" powerloss).
Using the brains is like using the Macropump it is an endless loop so if you program a saftey function that depends on an input to function it is possible that if the right conditions exist it could auto restart with movement.
As said the machine can absolutely not automatically restart. To restart the G9D relay requires a impuls action (non latching) key switch and a impuls action (non latching) start switch to be actuated at the same time by a human on the control panel. This can only be done if all ESTOP switches are out and all limit switches are overridden or not actuated.
Really this brain i request is by no means a safety function. It is simply a function to avoid loosing steps if a limit switch is reached. 
I have attached the datasheet for the G9D safety relay.