Not a rotator cuff but a broken shoulder.

They say 6 weeks in a sling, but they then told me after 3 weeks to take the sling off occassionally to stop the elbow freezing up.

As for 6 months of no cycling well- you can certainly get on a windtrainer early- I did it in a sling after 2 weeks!

I was lucky to have a tandem so after 4 months I was riding the tandem (it's good as I could rest my arm).

However don't rush things and let it heal properly or it won't be right. You can certainly use your legs so fitness wise there's nothing stopping you windtraining, spin classes, walking and even light jogging when you feel comfortable.

Also I know it's not nice to be off the bike, but you can also use your injury time to help out in the cycling world- be a supporter, turn up for coffee with your normal group, volunteer at races etc. Yes it sucks to stand and watch others but by yelling and supporting your friends you will still feel in touch and not left out, and you will find there's nothing like other cyclists to give you support through this time as well- they have most likely been there too.