I don't have any ideas on how to tell when it's a good time to go back to work except an observation that I could easily imagine myself never feeling ready to go back to work because I like not working a lot more than working (except for the lack of money)

Is a part time job or consulting work in your field an option? I did spend a few years not working and in hindsight think that it might have been better if I had kept up my skills by taking short term jobs or casual positions.