To be perfectly honest, you could decimate oncology, cardiology, and pulmonology (oh, and also save $$$$$$$$$) with one fell swoop by banning tobacco. Just throwin' that out there!
And yes, oncologists will be very much thrilled if this pans out. We're talking about a field where 30% of your patients die, even if you are the absolute best on the planet. That's what keeps people up at night. My interest in oncology (and in medicine in general), like that of countless others, began when I lost a wonderful friend to cancer after a decade and a half of increasingly painful but relatively successful treatments. It was the best anyone could do, but that's also what made it so unbearable, watching her become so fatalistic towards the end and knowing that, well, she was right.
It's not just a job.
That said, if this vaccine is wildly successful, I guess heme/oncs will be doing a lot more hematology, although there will still be cancer. "Treats 90% of cancers" will not translate to "reduces cancer rate by 90%" for reasons both epidemiological (this is a vaccine against a protein that all of our bodies can produce, and as such I don't know if it will be recommended for everyone the same way that the HPV vaccine is) and biological (if we do that, there will be an uptick in the rate of MUC1-negative cancers, probably small but statistically significant). The realistic view of "cured cancer" is something more akin to HIV; effective screening, regular followups, but ultimately a livable condition. These days, if you are diagnosed with HIV, the first thought through your mind isn't "oh my god, I'm going to die". It won't be a good thought, but it's just not a guaranteed death sentence anymore. That's what oncology is aiming for. There's plenty of work to do and chemo agents are problematic right now anyway, what with supply shortages and drastically lower reimbursement rates.
Every heme/onc has spent at least 8-10 years as an internist and they'll figure out something to do if it really does come to that. If there is a shadowy conspiracy to keep cancer alive, it won't be them.
The poor radiation oncologists, though, will be in for a shock. Theirs is essentially THE most competitive specialty, and they're basically separate from the rest of medicine because they're the ones who can do math, physics, all that hard stuff. They might raise hell.