Proof increases investor confidence, but that's hardly everything. Tesla contributes somewhat to open source, but ITAR and shrewdness means a ton of their tech is classified. If they folded, a great deal of that would be bureaucratically inaccessible, gone, or irrelevant. If we wanted to go to the moon again, we would basically have to start over from scratch. The Saturn V plans exist but the infrastructure, manufacturing techniques, and hardware are all gone.

Plans are 10% of actually building something, at that level. Materials aren't legos, each product needs to be qualified and have its idiosyncrasies addressed. Even at the consumer level, when you change manufacturers you often have to retool your process because while the specs are the same, you're delivered something different.

Keeping technology at the same level requires ongoing engineering. When that engineering is removed, the technology decays. It very quickly becomes a matter of reinvention rather than rebuilding.