I'm creating a website for a family friend who has a small business. They already have a leaflet that was designed a few years ago. To what extent should web/mobile design match an existing print design? If the print design does not work well in the web/mobile space ought it be revised in order for both realms to work well together?
There is certainly value in ensuring continuity between an organisation's print material and website. For one thing, if a customer goes to a link promoted on a leaflet and the resulting website looks completely different, the experience feels disjointed and lacks credibility. It's important for a brand to have a consistent customer experience across all channels, both online and offline.
That said, the print and digital contexts are very different so things like layout and typography will necessarily be different.
The UX Magazine article Investigating Cross-Channel Consistency makes this point quite well:
While the aspects of the look and feel that involve branding should be consistent with the ecosystem, the overriding style of the user interface should match its local habitat.
In other words, the look and feel of a brand should be consistent across all of its channels and materials but the interface (whether it's digital or print) should be designed to meet the strengths and constraints of that context.
One must understand the strengths of each medium. So what works for the leaflet may not necessarily work in store, which may not work in web / mobile as well.
There are some things that should be kept intact.
- Branding (trademark Information)
- Distinctive color palette
- Some of the typography if it helps identification of the brand personality
You have also mentioned that the leaflets were designed a few years back, you might want to consider uplifting the designs considering current trends keeping its core intact when you are transitioning towards web.
Bottom-line is, your brick and mortar store, its leaflets, website, visiting cards etc should clearly express that they belong to a single entity.