There are three parts to this question: how you answer this as a sales objection, how you answer this as a technical challenge, and how you answer this as a life challenge.
Sales objection: I'll try my level best not to get hit by any busses! No, seriously speaking, we have a written business continuity plan, which I'm willing to share under mutual NDA. In the event of my death or incapacitation, contracts fire and a well-regarded technical firm takes over the day-to-day operations of the business. You'll be able to export your data prior to the orderly shutdown or sale of the business, if that turns out to be necessary.
n.b. This assumes enterprise sales. If you're a $29 a month account, either you're OK buying SaaS or you're not. If you're not, I will not waste my time attempting to change your mind.
Technical challenge: Have up-to-date process documents in place for the major things and/or your major products. Get a buddy you trust and prepare an envelope with the In Case Shit Happens information in it. In my case, this includes passwords, SSH keys, and the like. (Pro-tip: your password to a password manager is far and away the easiest way to accomplish this.) You probably want paperwork between you to establish that they have legal authority to operate your stuff, and you'll want to have talked about what your priorities are. e.g. Should they just do an orderly wind-down? Should they keep the service in maintenance mode for as long as possible, given that you may recover? Should they try to sell the service for as much as they can, and give the proceeds to your heirs? etc, etc.
Your lawyer can help you think through these questions, draft the documents, and is a good choice for someone to hold your In Case Shit Happens envelopes.
Personal challenges: Estate planning is something you don't want to have to think about, particularly while young and healthy, but if you have loved ones or causes which would survive you, do it. It is highly likely that your business will, if it is day-job capable, represent >>> 90% of your net worth and take an immediate 90%+ hit to its fair market value in the event of your incapacitation.
I have a wife and daughter, and I want to see them taken care of, so I just have a term-life policy, covering ages 30 to 40 (I'm 32 now). The plan is, by 40, that I'll have socked away enough such that any proceeds from sale of the business would be "nice to have, but not critical" in the event that I encounter an untimely bus. If not, oh well, new term life policy.
This costs about $50 a month for a youngish man in good health, for $500k of coverage. You can get it cheaper outside of Japan, to my understanding. Get it, for the piece of mind if nothing else, if you have dependents.