SpaceX is not cash constrained. Every offering they do is extremely limited in terms of who they let invest, yet is still always massively oversubscribed. They're spending multiple billions per year on both Starship and Starlink but haven't been tapping the capital markets -- IOW internal cash flow is also massive.
Elon would also undoubtedly pour his Tesla money into SpaceX to keep it afloat. He's a lot more passionate about SpaceX than Tesla. But it's a moot point because SpaceX has a massively profitable monopoly on efficient space launches and probably will for a very long time.
