That is some bad luck with flight cases jazzyvee! Yikes! As demonstrated, there are no guarantees no matter how much effort you put into it. Same with trying to ship an instrument somewhere, there's always risk of damage or loss. The bottom line is; have up to date, all-risk, replacement cost, instrument insurance!
As you've found, trying to bring your axe onboard as a carry-on is a big roll of the dice. In-cabin rules for instruments vary widely, change often, and depend on how the gate staff and flight attendants are feeling that day. I am not interested in taking that gamble with the added stress of possibly being refused and forced to turn it over to the baggage handlers. I understand Jimmy Haslip always finds a way to get his bass onboard but he has three advantages: #1 his bass is much smaller than ours. #2 he is quite tall so the bass looks even smaller. And #3 he is a sweet guy and a very smooth talker. Ha!
I've had good luck with my ancient, slightly modified, aluminum, Zero-Halliburton flight cases when I need to check the bass. I lock all 4 latches and tape a key to the top of the case with "TSA >>> KEY" written on it and the key clearly outlined on the tape. If they need to open it, they peel back the tape, unlock it, throw in their "we were here" note, and lock it back up again.
But now I have to say - on these rare occasions when given an opportunity to buy an extra seat for the bass I will take that option. The instrument must be securely seat-belted in place. My cello playing pal asks for a seatbelt extension on his way into the plane so he can do just that. In my case, the regular belt fit through my old Reunion Blues backpack straps and that was enough to satisfy the flight attendants. Another plus, it didn't get drunk and try to talk my ear off for the whole flight.
Jimmy J