@goldenbyte
I don't think it's as straightforward as some people here think. A lot of people here suggest that once Model 3 is available nobody will be buying a Model S, which is not true (just because there is a 3 series BMW doesn't mean people don't buy 5 or 7 series ). I would be pragmatic and do the math.
The cost of keeping it is:
1. Storage insurance (you have to tell the insurance company the car will not be registered to be on the road)
2. Interest on the loan (not the whole payment, just interest)
3. Cost of storage (may be free if you are leaving an empty garage anyways)
4. Opportunity cost on any money you could get back (interest you could make on what you sell the car for minus the amount you owe today)
Cost of selling it is how much will you have to pay in 14 months to get back into a similar car. For this calculation, assume buying the very same car, upgrading to new is always extra. So, how much would it cost you to buy the exact same year, model, options, mileage in 14 months (find a similar car as yours that it 14 months older - how much less is it than yours). Subtract how much you can get for your car today (net after any sale costs), and you have your cost of selling and buying it again.
Without doing the numbers it's hard to tell which one is more beneficial. Also, there is always some risk as you are predicting future car value, which always has some margin of error.
If it was a longer period, I would think the difference would be greater. With only 14 months, hard to tell. As a point of reference, I sold my 2013 MS two years ago for 61K, a year later comparable cars sold for $50, so $11K depreciation in a year (another $10K depraciation for the year after that). So in your case, the depreciation may be ballpark $12K (discounting the "Model 3 will be the Model S killer" theories). That could be about the hit you would take by selling and buying the same car again (sale_price - trade_in_value).
Important note, if you were planning to upgrade to a new Tesla in 14 months anyways, then by all means, sell the one you have today rather than wait to trade it in 14 months from now.