Yes, a few that were disconnected from civilization, as stated by the creator of the show (8th bullet point under "jms speaks"):
There would've been a very few on deep space patrols, or on isolated worlds that would've survived, yes, as was indicated in the narration at the close of the episode, but you're talking about very, very small numbers. The race is still effectively dead.
Effectively dead because they can't recover. Here's some extra quotes from the same page as above, providing both in-universe and out-of-universe reasons that the Markab are all gone:
- Franklin's cure protects possible victims against attack, rather than eliminating the disease. B5, with its recycled air supply, now permanently carries the disease, which is dangerous to species with yellow and green blood-cells (or cells that perform a similar function, namely the manufacture of certain neurotransmitters) and might well mutate to endanger others.
"jms speaks" section:
- JMS: Spent substantial amounts of money making them the biggest single alien group we've got (some of the group shots had 40-50 or more Markabs, all in full prosthetics and full costume)...and now, never to be seen again.
- Anonymous: "No disease in human history is 100% fatal."
- JMS: Not correct. The Black Death was fatal to everyone infected by it. It was not, as Drafa, 100% contagious, but it was about 90% contagious. The Black Death wiped out three-quarters of the entire European population. (Editor's note: not quite true; three-quarters of the population in some areas was wiped out, but the total toll was closer to one quarter -- still pretty devastating. The mortality rate was high, but some people survived and were immune thereafter. It also hit Africa and Asia.)
- JMS: We joked a few times about having a mass burial for the Markab prosthetics and costumes behind the stage....
No more Markab prosthetics, so we'll never see them again, and the plague is still floating around since it can't be killed, so any of those remote survivors will die once they return to civilization. They're unlikely to know about the plague, so they wouldn't seek out treatment - and as shown by the bartender right at the end, a lot of people won't care enough to tell them about getting treatment.