[ossiblue]

It's not really clear in your OP if you made formal notification, during the initial build, that a porch/deck would be added. When I first read your post, I got the impression it was added without notifying the building department, but then you added the comment of the porch not being reviewed. Can you clarify?

Why didn't the final inspection pick up the presence of the porch if it wasn't on the plans? If it was there when the final was done, perhaps the inspector saw it as something that did not require a permit. Do you have a copy of your original plans with the porch added? Is it stamped for approval?

Most likely, not doing anything will not be an issue, but if you ever intend to sell or remodel, this will come back to bite you. If you have any documentation that you submitted a revision that included the porch, I would suggest you use that and apply for a variance and granting of a "non-conforming" structure. That would allow its legal existence, but might require a removal or rebuild if you should ever remodel.

Dealing with building departments can be a PITA, or can be very easy, especially in a smaller community. Again, if you have some way to show you submitted a revision, approaching the department, in person, to ask their help in resolving this issue may be the way to go.