about engines going to approach idle if both the genies drop off line .. its a guess but ( in a NG ) below 15000ft if the flap position feedback fails the engs got to appch idle...and with both genies off line the flap position indicator does not work.....
The go around question depend on how fast you work the MCP panel cause you go into ALT ACQ really early depending on the ROC... best option as the FCTM also recommends is to take over manually and level her off ..