Not true. Fine to be a solo entrepreneur, especially for more senior founders. YC may want multiple founders, but they cater to first-time founders.

> Lots of customers will want some assurance that if you die in a car crash on the way home, there is someone left to continue on with.

Another person involved does not improve the chances that the company will survive if you get hit by a bus. Releasing all the code as Open Source, or providing the source to existing customers is a much better way to mitigate risk.