Fig mosaic virus,like many other viruses,mutate if they need to ,to fight whatever might be after to kill them(imune system,medicine etc).If they mutate in a very succesfull variant,then it will survive and suck the live out,of a plant or animal.
Their goal is to live on the back of other organism,not to kill that organism,but like any parasite,it will affect negative ,and the organism will not flourish as it should.
Of course In our eastern climatic condition,where the fig tree has to fight the long period of frost,or life in a pot,adding FMV,burden to the plant will sometimes lead to total demise,death of the plant.
So to your question:Are there more than one FMV kind,the answer is yes:
There can be at least one other mutated more damaging Fig mosaic virus,additional to the original FMV,known in the past.