what does the output of ifft in ofdm look like?
You are correct that the output of the IFFT will normally have both a real and imaginary component.  That is fine and normal.  When the signal is modulated from baseband to the carrier frequency the real part is typically modulated by a sine wave and the imaginary part by a cosine (or vice versa).  This allows both parts to coexist without interfering with each other, since sines and cosines have zero cross-correlation.

Regarding how the numbers are represented digitally, they are represented the exact same way that real numbers are represented.  The only difference is that there is an extra set of numbers for the imaginary part of the signal.