I am not a lawyer or financial advisor but if money is not an issue then one could get a living trust and have trust managers renew your domain.
Some DNS registrars will let you pre-pay for 10 to 100 years. 10 years is the actual registry limit but some DNS registrars assuming they stick around will hold the 100 year credit on your account and continue renewing your domain on your behalf. This combined with a living trust could get you to 135 years. To go beyond that I think you would need to find a registrar that will honor your living trust and hand your domains over to a beneficiary. Get that in writing.
You may also be able to add a trusted beneficiary as a technical/administrative contact on your domains before you pass. It will be up to them to renew the domain. They could repeat the process adding their beneficiary to the domain.
This of course does not take into account things like your hosted services. Some VPS providers will also let you pre-pay into the account to keep it active. Each VPS provider appear to have a different upper limit on how much credit they will hold. Someone will need to maintain your services as protocols, methods, api's, etc... will evolve or devolve with time and may be deprecated. If your service is hosted somewhere they might handle this assuming your code works with the newer protocols.
