Hi! Until someone comes along who is more familiar with the contemporary sources comes along, you might want to take a look at an old answer I wrote about how the Black Death works here, and plenty of people who contracted the disease survived. It doesn't have a 100% mortality rate.
As to contemporary accounts of what it was like, you might want to try Giovanni Boccaccio's account of the plague's arrival in Florence. Unfortunately, contemporary sources are rarely around on the internet free for everyone to read, but that one is.