Transferring coded website to another owner

Hi there! I'm building a website for a client which includes coded customisation. I'm building it on my account, which is on a Business Plan, and will be transferring ownership to them once it's complete. 

Once they have ownership of the site, will they too need to have a Business Plan in order for the coded sections to work or will they be able to continue using a Basic Plan? (Assuming that no additional code will be added to their site once ownership has been transferred...) 

Thanks so much.