The 'E' model is generally considered to be used in non-stop&go (urban traffic) environments. Therefore, like many KTM EXC/XC models . . . it has no fan.
Unlike the higher strung KTMs the DRZs (and the 'E' is slightly higher strung with a different cam, FCR carb and slightly higher compression ratio from a thinner base gasket) other than the 'E' all come with a fan.
It's use is of value in stop&go and higher ambient air temps. My DRZ fan kicks on in Thailand rarely, even in urban riding.
There's a company which makes larger capacity radiators for heavily modified DRZ engines (big bore kits, hotter cams, higher compression, etc). These are considered completely unnecessary except for highly modified DRZs or unless you make a point of riding in desert sand dunes.
A well-respected DRZ tuner maintains that the DRZ cooling system is capable of twice the heat exchange load that the OEM engine can deliver.
So . . . if it were me, I wouldn't worry about the fan unless you're in alot of stop and go in high ambient air temps. You could always switch the engine off in those cases.
However, I also find the kicker option on the DRZ unnecessary. So I'd keep the fan and save the worry. At least try a kicker before you go through the expense and work. It's a commonly debated "add-on" in many forums and largely foregone.
Orange, it's the new black.