Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of employee],
You've made strong contributions to this organization in the past, and I just wanted to check in with you to ensure you have everything you need to continue to excel.
I spoke with HR and they mentioned that you have [number of days] days in available vacation time. Since we're not too busy at the moment, you're welcome to use some of that time if you'd like.
If not, is there anything I can do to help? From a personal standpoint I feel like you haven't been your usual cheery self, and we all kind of miss that person.
If you need to talk, my door is open. You're welcome any time.