Is there a constant for the Maximum Unsigned Long value in an Arduino compiler?
Various limits.h files in the avr-gcc hierarchy define ULONG_MAX, which may be the value you want.  For example, on my system such files have paths ending with hardware/tools/avr/lib/gcc/avr/4.8.1/include-fixed/limits.h or with hardware/tools/avr/lib/gcc/avr/4.8.1/install-tools/include/limits.h and contain definitions like the following.

/* Maximum value an `unsigned long int' can hold.  (Minimum is 0).  */
#undef ULONG_MAX
#define ULONG_MAX (LONG_MAX * 2UL + 1UL)


Note, LONG_MAX also is defined in limits.h.

Note, arithmetic done in a form like

timeDelta = micros() - prevTime;


will be correct (regardless of whether micros() overflowed) for elapsed times up to 2³² microseconds, or about 4295 seconds.