Far less customers.
If their customers can't reach/find them, they will go elsewhere.
Not having an internet presence is commercial suicide - akin to not being on the telephone.
They can't be hacked.
It depends on the business. On line activity provides a means of access to a business. The business itself still has to be sound. A beautician can have on-line booking but the service is always hands-on. Undertakers may provide access via an on-line portal but the service remains in the real physical world. Presence on-line is useful for advertising our existence, promoting our goods/service, giving access to stock lists and providing a sales portal..Companies like Amazon could not function the way they do without an on-line presence so, for some types of business, being on-line is essential. For others, it is probably beneficial because it makes it possible to reach much wider marker than non-on-line trading could achieve.