Hello Wkoziol,
At first, this sounds like a bug that randomly affects the sims. What troubles me is that it has happened on two consecutive occasions.
I can only give you a few suggestions and hope that one of them will help.
If you arrive in the WA destination and your sims are not there, it can often be fixed by selecting edit town. Then select your home town from the top left. When you get to edit town (your home town) select one of the community lots for editing. Pick up an item, it does not matter what, and place it back down. Return to edit town. Select return to game. This should force the game to reload your vacation destination and with a bit of luck, your vacationing sim/s. Do not save during this process.
Check your sims3 saves (under documents) for .bad files. If you have any of these delete them.
This is more complicated, but, it has helped me in the past with this bug. Replace your sims WA meta files.
http://www.carls-sims-3-guide.com/forum/index.php/topic,6.msg265556.html#msg265556The instructions are about half way down - message 87.
My final suggestion is to do a factory reset, but, I am not confident that this will fix it. However, it will definitely clean-up and speed up your game and it takes just a few minutes.
Good luck, and please let us know if this doesn't help. others may have better suggestions.