@Kyudos
The sale of individual Autodesk product perpetual licenses ended as of Feb 2016. The sale of Autodesk suite product perpetual license end Aug 2016. From that point on, you can only subscribe (purchase) to commercial license based on a single user or multi-user subscription (term) based license. Subscription rules allow for the user to use the current release (at this time would be 2018) and 3 legacy versions (2015-2017).
For those who have an active maintenance plan (meaning continuous paying per requirements) for perpetual licenses, the same rules apply (2015-2018). Around the April/May time frame for 2018, Autodesk would be releasing the 2019 product line. If you still have an active maintenance plan at that time. You would then be entitled to 2019-2016. The 2015 product line would be obsoleted by Autodesk and no longer supported and thus you wouldn't be entitled to it unless you get an exception for Autodesk. Now at some point in time (in the future), the same thing would happen to 2016, 2017, and etc.
Ok now that I've rambled on.. Let me answer your question... 
When you drop your maintenance plan the rule is.. You are only entitled to the current release that Autodesk has. Meaning if you dropped it tomorrow, you would be only entitled to the 2018 product line. However it also states its based the last activated version. So it you activated 2017 and drop maintenance tomorrow, you would only be entitled to use the 2017 product line. But I've seen cases where Autodesk just deactivates all the legacy versions and you're only entitled to the current release like I already pointed out. In the end when you drop your maintenance plan you lose the ability to legacy versions of the product. If you want to come active again you would have to move over to subscription based type of license.
But I guess I have to ask if you are developing ARX programs, are you making money of these programs? If you are, why would you jeopardize your business by dropping your maintenance plan? Wouldn't you want to support you end users? Not sure what you are developing, but have you every consider the Autodesk Development Network? I don't know all the licensing aspect of the ADN, but you may have more control over your license since you are developing programs that are for Autodesk products.
Not sure if I helped you out or not.. Perhaps you have more questions now because of my reply.
Mark Lancaster
& Autodesk Services MarketPlace Provider
Autodesk Inventor Certified Professional & not an Autodesk Employee
Likes is much appreciated if the information I have shared is helpful to you and/or others
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