Refer to figure.
EASA learning objective 022.06.05.01.06 states: 'Explain the purpose and significance of alert height, describe the indications and implications, and consider typical pilot actions for a failure situation: above the alert height; below the alert height.'
EASA learning objective 022.06.05.01.07 states:' Describe typical failures that, if occurring below the alert height, will trigger a warning: all autopilots disengage; loss of ILS signal or components thereof; excessive ILS deviations; radio-altimeter failure.'

Althought the question doesn't state it, if you're below 100 ft on an autoland approach with a fail operational system you are below the alert height! The alert height is based on the aircraft's characteristics and its fail operational automatic landing system and varies between 100 ft and 200 ft depending on aircraft type. The alert height determines the pilots actions in the event of an autoland system failure:

• If a failure occurs above the alert height, the pilot must discontinue the approach and perform a go around.
• If a failure occurs below the alert height, the pilot can continue the approach unless the AUTOLAND red warning light illuminates

The question makes no mention of an autoland warning but states that 'the glideslope indication disappears'. It's important to note that below 100 ft the loss of the glideslope signal will not trigger an autoland warning becase the system will have already gone into an 'attitude hold' phase until 70 ft radio altitude where the radio altimeter takes over vertical guidance. Localiser signals are more important as they're needed for runway alignment and will trigger a warning right down to 15 ft RA if lost.

According to the Airbus A320 FCOM regarding ILS signals the AUTOLAND warning flashes when, at least one RA indicates a height below 200 ft, at least one AP is engaged with LOC and G/S, LAND, or FLARE mode on the FMA and at least one of the following conditions occurs:

• The LOC deviation exceeds 1/4 dot and the aircraft is above 15 ft RA (the LOC scale flashes on the PFD), or
• The GLIDE deviation exceeds 1 dot and the aircraft is above 100 ft RA (the GLIDE scale flashes on the PFD), or
• Loss of LOC signal above 15 ft RA (the FD vertical bar flashes on the PFD), or
• Loss of GLIDE signal above 100 ft RA (the FD horizontal bar flashes on the PFD)

Base on the above information the correct answer is continue the approach as normal. You could argue that to go around would be the safest option but the statement '.... and the system becomes passive' is incorrect because without a glideslope signal there is no autoland capability at all wheras 'fail passive' refers to the redundancy capabilities of a working system!

Given that autolands are carried out in conditions of low visibilty, taking over manually isn't an option if you can't see the runway! Requesting assistance from ATC is never a correct answer!