When Bernard Labadie returns in December for his first engagement with the Chicago Symphony Orchestra since May 2014, he will be making just his second public appearances anywhere since an 18-month medical hiatus due to cancer. He’s not just fortunate to be back on the podium, he’s also lucky to alive. “Almost against all odds, it did work out,” he said.

A week after his 2014 concerts with the CSO, the French-Canadian maestro fell ill in Germany and was diagnosed with T-cell lymphoma — a kind of blood cancer. He was in the hospital there for a month before returning to his hometown, Québec City, for what became a grueling medical odyssey.  He began with the usual treatment for this disease, a transplant of his own blood-forming stem cells, but this approach did not work. So he required a more complicated and more dangerous stem-cell transplant from someone else; one of his three siblings — a sister — proved to be a compatible donor.

The procedure took place in October 2014, but things did not go well. “Basically, I got every complication that is possible and then some,” Labadie said. Along the way, he had to be placed in an induced coma for a month, and when he was finally awakened, he faced severe muscle loss. “So when I woke up, I couldn’t hold a glass of water,” he said. “I couldn’t turn in my bed. Of course, I couldn’t stand by my bed or get up.” Thus he began an arduous rehabilitation. Labadie finally left the hospital in April, and he has continued a range of physical therapy and physical training since. “But things are going well,” he said. “It’s just a very long process.”

Labadie does not expect to be back to a full schedule of conducting for at least a year, but in the meantime, he has received the green light from his doctor to begin limited engagements. They will begin with back-to-back performances of Handel’s famed oratorio, Messiah, starting Dec. 3-6 with the St. Louis Symphony Orchestra and continuing a week later with the CSO and Chicago Symphony Chorus for five performances Dec. 10-20. He will have the same hand-picked soloists for both engagements: soprano Lydia Teuscher, mezzo-soprano Allyson McHardy and tenor Jeremy Ovenden. Bass-baritone Kyle Ketelsen replaces the previously announced Philippe Sly, who had to withdraw due to illness.

Labadie believes that he is ready. “I’ve run some tests,” he said, “and I’ve done some air conducting, if I might say so, and it seems to be working.” But he will make one concession to his weakened condition and will remain seated while conducting.

The maestro chose “Messiah” for his return, because he knows the piece so intimately, having conducted it at least 150 times with more than 20 different ensembles. “Artistically, there is not a lot of pressure, let’s say, compared to new rep or things that are a little less usual,” he said. “And these are soloists who I know very well. So the idea was to gather the best circumstances for my return, so I feel confident. St. Louis and Chicago are two orchestras that I’ve conducted regularly. The musicians know me. I know them. I think we trust each other, so I think that should take some pressure off when I come back.”

As he always does when he comes to a modern-instrument ensemble, Labadie will try to instill at least a partial period approach to this Baroque-era oratorio, which means a lighter, more transparent sound with considerably less vibrato and brisker tempos. “Certainly, I will ask the strings to have a different approach to sound,” he said, “and I know the Chicago Symphony players can do it very well, because I did St. John Passion and Water Music with them, and I remember vividly how good they were at switching gears and being completely open-minded. It’s not sound only. It’s a lot more than that. It’s the whole concept of articulations, bowings, all these intricacies of a language, which is quite different from their usual language. And great orchestras like the Chicago Symphony love to indulge in that. It’s a challenge for them to speak in a different language within a very short period of time.”

The big news for Labadie before his illness was his decision to step down at the end of 2013-14 after 30 years as music director of Les Violons du Roy, a well-respected, period-style chamber orchestra in Québec that he established as a 21-year-old upstart. “Of course, I could have gone on,” he said, “and when I made the announcement, it was a big surprise for everyone, but I think it is wisdom to actually leave when people don’t want you to leave and not to wait until everybody’s praying, ‘When, when is the old man going?’”

He now holds the title of founding conductor and plans to lead eight weeks of concerts a year with the group, allowing him to still maintain a strong bond with his longtime colleagues. At the same time, he will continue as head of the orchestra’s sister choir, La Chapelle de Québec. “So I’ll still be around, but I won’t be in charge of the big artistic decisions, and that’s totally fine for me,” he said.

Once he is totally healthy, Labadie plans to devote more time to guest conducting — perhaps four to six months a year — and he is looking forward to the freedom to pick the orchestras with which he wants to collaborate and the projects that catch his fancy. He does not foresee pursuing another music directorship unless something “really special and unusual” comes along. Because he concentrates on a 150-year swath of music, essentially the late 17th through early 19th century, he believes he would be suited to helm only a period-instrument ensemble, and few such positions ever come open.

At the same time, his specialization all but precludes him from being the leader of a conventional orchestra that plays a broad range of repertoire. He does not, for example, conduct contemporary music, which such ensembles typically take on from time to time. “Not that I don’t respect it,” he said. “On the contrary, I respect it probably too much to do it, because I’m honestly not very good at it. I’ve done some in my early years, and it was a lot of work for me, and I didn’t feel like the results were there. I always felt there were lots of people doing it better than me. I think we have enough charlatans in my field, and this world doesn’t need another one.”

Labadie is always happy to come back to the Chicago Symphony. But this year’s reunion is very different. It marks not only the end of what he called “a pretty horrific year and a half” but also a long-overdue return to some semblance of normalcy.

Kyle MacMillan, former classical music critic of the Denver Post, is a Chicago-based arts journalist.

See a related fetaure on WFMT.com: How a Modern Orchestra Plays a Period-Perfect Messiah