Actually the Super Heavy (first stage) already uses heavy CO2 based fire suppression. Hopefully not that necessary in the long term, but should make it possible to get on with the testing in the short term.
What is a long term solution for this? Is there something more than "build tanks that don't leak"? I'm sure spaceX has top design and materials experts, now what ;-).
I think its likely not the tanks but rather the plumbing to engines and the engines themselves leaking (sense lines, etc).
Next engine revision (Raptor 3) should help, as it is much simplified and quite less likely to leak or get damaged during flight.
That's interesting
However if you see the stream you can see one of the tanks rapidly emptied before loss of signal
It seems this was not survivable regardless of fire or not