Based on your description, it sounds as if you have some possible decay under your veneer. The consequence of doing nothing about it, will likely lead to you losing the tooth. There is a possibility that when your dentist removes the veneer, he/she will determine that the tooth needs to be extracted, but there is also the same possibility that your dentist will determine that the tooth can be saved. However, doing nothing will only make extraction more likely in the immediate future. Good luck and I hope this helps. Follow me if you have more questions.
Sarah Thompson, DMD
The ONLY way to know what is going on and how much tooth remains is to LOOK at it. Directly. This requires removal of the old crown and the only way to get it off is to cut it off (totally destroy it). If an implant is the next step, rest assured that an experienced clinician can make it virtually painless and the implant should last a very long time (it is the longest lasting treatment in dentistry).
It is very difficult to give you an accurate opinion about what is happening with your tooth without being able to do an exam in person. However, usually when a tooth that has a post is moving but not falling out it means the cement that is holding the post has failed and the post is loose. This is not a good thing as decay can move down the post space fairly quickly. I suggest you have your dentist check this ASAP. If he does not see a problem a second opinion might be a good idea. Good luck.