Advice for resuming riding after illness?
There are stages to recovery from any illness (or injury, for that matter).

After surviving the incident and any medical intervention, we hopefully get to the rehabilitation stage. At this point, we're usually weak in a muscular sense, and feeling weak too.

The type of rehabilitation we undertake now has a big bearing on the end point we get to. It's all about goals. Do your goals match your rehabilitation therapists goals? If there is a mismatch between your goals and their goals then you will find the whole process quite frustrating. So have a good talk with potential rehabilitation therapists about what you want to achieve, what they think about that. If they think you're crazy get them to explain, or recommend a colleague. Patient - therapist communication is key.

Let me digress into few small anecdotes before returning to some recommendations


In my 20's I had a knee injury. The injury was responding to treatment, and the physiotherapist I was seeing wanted to measure my knee strength. Strapped me into a machine and said "push as hard as you can". Bang! Total recurrence if the injury. They omitted "without discomfort".
Another knee injury. Surgeon discusses options with me, and says "We could operate, but since you're not a pro athlete I don't recommend it". Good call. I learned to play squash much better than before, because I kept on my toes more.
Tore a calf muscle last year. Right through. My physiotherapist is a former pro footballer, a high profile guy. As my physio for 30+ years, we understand each other well. He knows my goals, my particular level of pain tolerance, my particular level of determination. It's a close relationship. He tells me straight what the prognosis is, how much work it will take, and how much time. Working together, I was back cycling in six weeks. But a year later, not back to full strength. Perhaps it's to challenge me, but he says I'll never get back to full strength.


The point I'm trying trying to make in each of these is that rehabilitation is a partnership. Each therapist has their strengths, weaknesses, interests and focus. 

To get to your goal, you need someone whose goals match yours. More importantly, someone who admits where their knowledge or experience ends. And a willingness to call in others who may have the necessary knowledge or skills to help you. So you'll have be open about your goals, and openly search for a therapist who you can really relate to. Communication is key

Oh, and one more thing. Indoor training has come a long way. Check out BKOOL and Zwift.