You can't buy a used license, per the current terms. If you buy the company, you get the license, but you can't transfer it or buy it from him. That said, as long as you're not going to try to get/keep it on subscription, or you just walk in to you VAR and pay cash while pretending to still be employed, you can probably link the license to your SolidWorks customer portal login, which can use whatever email address you want.
Depending on the country you are in, you could perhaps buy it. There are some countries in Europe as far as I'm aware that allow this, tough I think it is frowned upon by SolidWorks.
It's linked to the company that bought it. In general the license agreement says it can not be resold. As Alex mentions, some countries (particularly in the EU) make such license restrictions null and void, hence in those countries software is a tangible good that can be bought and sold.
Now, the license in use is tied to the computer from a technical point, but if you were to move it to another computer or renew it, then you would have to do so as a representative of the owning company.