Based on the reported behavior for the Sony SLT-A55, the camera will still operate and take photos even if the translucent mirror is up or removed. However, autofocus no longer works, since the SLT phase-detect AF system depends on light being diverted by that mirror to the AF sensor. There’s no indication from the provided answer that it falls back to contrast-detect autofocus.

Exposure is also affected: with the mirror out of the light path, images are reported to be off by about 1/3 EV. That makes sense, because the translucent mirror normally steals a small amount of light for autofocus; removing it changes the amount of light reaching the imaging sensor. So in practice: shooting still works, AF is lost, and exposure may need compensation of roughly 1/3 stop.