I assume you are correct about the non-compete though you will probably need lawyers if they attempt to intimidate you. If they have a patent on any of the software you could be in trouble if the features you decide to re-engineer are included in the patent. Otherwise, I would document your requirments and design very carefully so you can demonstrate how you developed your product and why it is in the marketspace it is in. It is quite possible that your employer is going to be hoping mad and looking to inflict as much pain on you as possible since you exit may be the best way to explain their failure. Of course if you stay, you will probably be blamed anyway. In situations like this, in my experience, the incompetants always are on the lookout for someone else to blame. Good luck