Odds of Hanging On
The whole "no shortage of jobs and patients" thing means you already know the odds of hanging on are good. They're very good. The biggest obstacle you'll face is burnout—and that's a real possibility. If you can't avoid burnout through careful stress management, a healthy lifestyle, and some well-timed vacations, you can always switch from practicing oncology to researching or teaching it.
Plan your career well, and you could take it in any direction you want it to go. You could work in a private practice for years, you could mentor students and do research at a teaching hospital, or you could teach seminars or medical school classes. There's no worries about hanging on. You just have to decide where you'll do best.