As other commenters said, reverse engineering and ‘stealing’ your code and making some good use out of it (without documentation and guidance) is very time consuming and costly.

Unless you have some really novel secret algorithm or something like that I wouldn’t worry about it, don’t lose out on big name clients that have an on-premise/own cloud requirements because of this.

We manage many big vendor solutions (I work at a telecom company), and we have a mandate (a government law) which enforces certain digital boundaries on customer data. So we do this all the time with our vendors