I second this. Code without people expertly familiar with it is a liability and a risk, with unbounded/unknown associated long-term cost of training, further development if possible, or a rewrite (in which case starting from scratch anyway), and maintenance.
..Then perhaps it can be recommended for the OP to "sell" the code together with the expertise/team/himself as a package?
If I were in a situation where my company needed a solution that he describes, I might be interested in such a package: fully functioning software with a domain expert (who has proven able to put together and lead a team).
Maybe, maybe not. A codebase that hasn't been integrated into your development process and is completely unknown to the development team is as likely to slow down your company as speed it up. At least if you write it from scratch you learn a lot while writing it, you have deep knowledge of how it works, and your team isn't pissed off that they need to suffer through someone else's legacy software.
I've seen plenty of ground up rewrites work, but I have almost never seen legacy software moved to a completely new team successfully.
The other guy seems to believe that the business can survive with a designer and a shopify site. Maybe he's wrong, or maybe the existing customer base and relationships are the real value here and the code is worthless.
Code is inflexible. Code has bugs and vulnerabilities and patent infringements and licensing issues. Code needs lots of maintenance.
The value is in the people who know the code. That's you. If you sell the code, you have to go along with it.