A well built 40 spoke wheel with a decent cassette hub is unlikely to fail whereas it would appear the 48 spoke wheel with the freewheel already has... the axle on the 48 spoke wheel is the weak point and bet the wheel itself could survive armageddon.

The cassette hub is the way to go and being that you are dealing with a 26 inch wheel that 40 spoke wheel should be damn near bombproof.