They are much less likely to develop the disease a second time.
Memory B cells help your body prevent getting sick a second time once you get sick the first time. So for instance it may take about 15-16 days for your memory B cells to produce enough antibodies against this certain pathogen the first time, however once you get sick with the same thing the second time, these memory B cells will kick in and will take less time to fight off the pathogens in like 5 days. :)
Lymphatics and immune system is very important to study :) hah
Good luck and I hope this has helped you! :D