That’s an excellent question. Ideally it’s something you should discuss with your therapist but I’m guessing you probably have.
I think it can be helpful to have the option to share your thoughts and feelings with your therapist while they are away. I don’t mean having a phone session or exchange but asking if it would be ok for you to send them emails or leave phone messages without expecting a reply.
Many therapists have someone cover for them while they are away. This is generally utilized for crisis situations but I’ve had some clients who wanted to schedule a session or two with another therapist while I was away. This would give you an outlet to express your feelings about missing your therapist with another clinician.
It’s also helpful to plan for such absences by making sure you are particularly busy or doing things with others. Anticipating your feelings, distracting yourself in healthy and positive ways is an excellent way to get through a potentially challenging time like this.
Some people find it helpful to know loosely where your therapist is going so they can imagine them in a positive setting and remind yourself that they will be coming back. It can be reassuring to know that they are safe and possibly having a good or relaxing time during their absence.
You can use a journal or some other creative outlet to express your thoughts and feelings while they are away. You might even plan to share your creations with them when they return, which gives you a project that also keeps you connected to them.
If it’s an option you can also take a vacation yourself at the same time. This is how people did it back in the Freudian days of psychoanalysis. They were expected to time their vacations with their therapists. I realize this is not very realistic for most people these days, but throwing out every possibility here.
That’s all I can come up with off hand. Hope some of it is helpful to you.