Nowadays to get such biocontrol agents released a lot of experiments have to be done whether it will feed on related native species and / or important crops as well, only when that is not the case, they may be introduced....
But the option cannot be excluded totally that it will not adapt once released and the initial food source is low in abundance. Examples that something like that happened are however very rare since proper testing in advance was introduced... (that was clearly after the Partula disaster...)
But with only biocontrol as control measure to combat Carrazzo will never disappear completely, there is not a single biocontrol case that has completely let the target species disappear, although there are examples in which cover was brought back to an acceptable level, other control measures should also be implemented to really get rid of Carrazzo (which is probably impossible...)