I've been in atrial fib for 15 years, on warfarin the whole time, and if my experience is typical, your life isn't going to change much. I'll be 60 in January, and I still ride regularly, do everything I did when I was in my 30s and 40s, and I've survived a couple of epic falls with no more problems than some pretty spectacular bruises.
You WILL find that your speeds decrease, I imagine. I was primarily a runner when I was diagnosed, though I'd ridden off and on for years. When my 10k time went from the high 30-minute range to 45 minutes plus, I moved more into cycling because I had no previous times to make me feel bad. I average 175-200 mi/wk in summer, do a couple of centuries every year for fun (?) and haven't had any more problems than other guys my age. I did my fastest 50-mile ride ever in July, at age 59 1/2 (it wasn't FAST, but it was faster than I could do 20 years ago).
Regarding the cardioversion: Technology may have changed since the last time they tried to convert me, but my heartbeat didn't change at all. With luck yours will, but it's not the end of the world if it doesn't.