I think therapists do expect to be missed when they are away. I also believe they are okay and some even happy - when clients tell them about it.
The harshness with which people here judge themselves and others (clingy, needy, overwhelming etc) is off base I believe.
First - therapists set the game up so that it happens. Some even arrange for back up therapists for their clients to contact when they are away.
Second - I think most of them expect it and can handle it and some even like it and find it gratifying that they are so needed
Third - just having the feeling and acknowledging it is very very different from acting on it in an inappropriate way - and in therapy - it is not inappropriate to cry, tell the therapist, storm out etc. (I think showing up at the airport or the vacation resort may be going a bit far).
Fourth -it can be good, from what I have read, for some clients to see that their feelings about the therapist/situation do not destroy either of those things.
Fifth - even though it may feel like one cannot cope with the therapist being gone - most people do in fact - survive it. Thus the belief that one cannot cope is proven false - one can.