The only worthwhile visual info. you'll get off a low-pressure tyre is likely to be below 15 PSI in the case of a car, it's nearer 6 psi.........anything over and the tyre LOOKS normal......a gauge is the ONLY way to check pressure accurately...a pilot's walkround is, by the nature of things, fairly superficial (was going to say cursory) Any tyre appearing to be "flat" is probably already weakened by the landings /takeoffs since it lost pressure.
IMO, delay the flight, change the wheel/tyre assy.......then the Engineers can load-test it at their leisure in a cage.
The victim of this sad incident will now be severely hampered in his efforts to make a living. glad to hear he's on the long road back to recovery.