Reactive windshear is available up to 1300ft, predictive 1800 or 2300 depending on the weather radar.
Since A.FLOOR is available from lift off to 100ft RA, I'd imagine it will be activated if the conditions are met. The right thing to do probably is to put TOGA on realising that the speed is reducing rapidly, to try prevent putting the aircraft in that situation, and not wait for the w/s warnings even if it's within the warning envelope.