Mate, nobody disconnects the autothrottle by turning off the A/T Arm switch (unless you've lost an engine). You must surely know you just use the A/T disconnect switches! Thereafter, assuming you haven't been below 5' RA for 2 seconds (or whatever it is....irrelevant here), pushing the TOGA switches will give you 2000 fpm or TOGA power on the second push of the switches.
Really? I suggest you try this next time you are in the sim. Or, next time you disconnect the A/T (on thrust levers) out on line have a look and see where the ARM switch on the MCP ends up.
Centauras is spot on.
FCOM 4.20.8
Any of the following conditions or actions disengages the A/T:
• moving the A/T Arm switch to OFF
• pushing either A/T Disengage switch
• an A/T system fault is detected
• two seconds have elapsed since landing touchdown
A/T disengagement is followed by A/T Arm switch releasing to OFF and flashing red A/T Disengage lights. The A/T Disengage lights do not illuminate when the A/T automatically disengages after landing touchdown