It can be done in mono, and with actual amps miked up, but....you are going to hate it. Not to mention cheap 1 or 2 driver in ears. Plan on some frustrating times before you sort it out. I wouldn't say that if I hadn't gone through it, and more importantly, seen other bands go through it. In ears work the best when you can isolate each instrument, and you don't have open mics onstage (except vox and drums with iso shields). Also, everyone in the band has to commit to doing it properly.
Usually, most people go to in-ears because you hear better, and the stage volume is too loud, instruments onstage are competing with the PA, and you want better mixes out front. In the end, you wind up bringing less gear to the gig. But it is not just a commitment to switch to in ears...you fundamentally have to change your thinking how you get a sound on a stage with the band.