Thanks for taking the time to comment!
Yes, there is a chance they could roll a 0, which is why there's the opportunity to pay to consult again. Depending on where you've prioritised spreading the infection, some players may be forced to consult. Eg, Cats with infected sawmills cannot generate wood, WA with infected sympathy cannot revolt, so they are pressured into consulting at the start of their turn so they can take their regular actions more freely. The counterbalancing idea to that is that the more they consult, the more antidotes they gain, becoming less and less reliant on the healers as the game goes on.
There is certainly a risk it could be frustrating for players to roll a 0 and have to pay again. I tried to make it a bit nicer by allowing payment to be any card, item or (in desperate circumstances) a VP. But perhaps the roll could have a +1 effect like attacking defenceless tokens so you would effectively roll between 1 and 4 and it might not feel as punishing.
I think balancing the speed of the infection growing Vs the ease with which players can counter it would be key (and probably need a lot of playtesting and tweaks!)