We are [shocked and] sorry to hear about your [illness / accident]. [We are glad to know that [you are not hurt that badly / the illness is not as serious as first anticipated.] Just want to let you know that we are always thinking about and praying for you. 

[Although your presence will be sorely missed, do not worry about getting back to your job for now. We will try and find a way to cover you. We do want you back of course, but not until you have fully recovered and the doctor has given you the green light to return.]

[We will [give you a call] / [be seeing you in person] when you feel better. Do let us know when it is permissible for you to have visitors, and we will drop by to see you.]

We hope that you will have a speedy recovery. In the meantime, do let us know if we can you assist in any way. We will stand behind you and provide our full support.  

Good luck to you [on your speedy recovery / on your operation]!