Hate to hear this kind of thing and hope that everything works out OK for you.
I can only agree with everyone who has already said that you need to explain to your cardiologist how much riding means to you – there are other medication options that should have less effect on your capacity to exercise then bisprolol, and it’s worth exploring them with your doctor.
Things you could ask about are digoxin and amiodarone, as well as different beta blockers, such as sotalol.
Warfarin does increase your risk of bleeding after falls but, when it’s stable and in the right INR range, is definitely no reason to confine yourself to towpaths.
Again though, what I would really recommend is talking it through with a doctor who knows your medical history (it’s easy for us to suggest things on the interwebs that might not really be practical) and making sure they know what your goals are. Most people with AF aren’t interested in exercise, and so your cardiologist needs to know that you are.
Good luck!