In real life if the fire warning goes out - whether after the first bottle or second bottle - assume nothing. Do a fire warning system test. If it does not test there is no guarantee that the fire is out (personal experience, related elsewhere in these forums). If you have reason to believe that fire is still present, land, NOW...if that means there is only time for speedbrake armed, gear down, flaps 15, add 15 knots, cabin alerted, so be it.
Disagree with you there, irrespective of whether the indication goes out or not, or if you believe the fire to be out - you land ASAP, as per the QRH. Even if the fire goes out, you have no way of assessing the damage.
Wasting time performing a fire test (albeit seconds) is just that, wasted time. It could also lead you into a situation of confirmation bias, where you now believe the fire is out and have more time that actually do.