Bankruptcy is kinda deep to talk about as most of the countries even if they are very poor will likely to create a counter measure in order to avoid this kind of happening as it is the worst. A country that is bankrupt is almost dead but the poorest country will likely to be hit hard if in case they will be affected that much by the virus and they can't contain it.

So it's a matter on how they are going to deal with the virus, other are imposing lockdown to lessen the affected person therefore all will depend on how the government will take a counter measure to this pandemic until the vaccine will be available. Even the wealthiest country are not exempted to this especially if they mismanaged this situation like what happened to USA where the infected persons are keep on growing. So in the end, I will not try to guess if who is the first country to become bankrupt as I don't like the idea and if possible I don't want any countries to suffer a bankruptcy.