How will they be able to deactivate licences if they decide to switch computers and old ones are not accessible to deactivate the product or if they upgrade hardware and forget to deactivate the software prior to upgradig?
As long as they still have the old hardware they can deactivate your product from it. Even if it means they have to reinstall windows and re-activate your product on the old computer. Then they'll be able to de-activate on the old computer. After that they can simply install and activate on their new computer.
For customers that have lost access to their old computer, then you'll need to de-activate them in LimeLM (which means you'll need to re-enable your LimeLM account for that action -- you can cancel again afterward if you want).
After a few years I've decided to stop selling new licences
Are you switching to another licensing product? Are you unhappy with LimeLM? Or are you just discontinuing selling the product?