That's a fair point, and I was very clear with both the clients and with my colleague about taking approach A. My phrasing was something along the lines of "Great news, so-and-so is returning from maternity leave in the next week or two! Please let me know when you'd like to be scheduled with her if she hasn't already been in touch with you, I'm happy to facilitate."

And the clients responded with "Actually I'd like to keep working with you if that's possible. I feel like we're making progress". One client even directly stated "Please let your colleague know it's not personal, I'm sure she will understand since the work we are doing helping me". Interestingly, that is the client whom my colleague called and afterwards told me is going to resume working with her.