Without seeing some sample data it's hard to tell what you want the formula to do.

Maybe all you want to do is replace the formula blank like this:

=LOOKUP(REPT("Z",255),CHOOSE({1,2},"NO_DATA"....

On a side note...

I would replace both:

REPT("Z",255)
9.99E+307

With:

"zzzzz"
1E100

=LOOKUP("zzzzz",CHOOSE({1,2},"",LOOKUP(1E100,......