Air carrier pilot reported observing another aircraft perform a missed approach due to runway incursions at MHR airport.

Narrative

We operated into MHR this morning and landed at XA am.The Airport Briefing guide says the tower was open. We were caught off guard at the last minute when ATC gave us the normal cancel upon landing. Phrase. I immediately started making normal radio calls on CTAF.We were following the ILZ Z 22L approach in VFR conditions. We were surprised to find that we had a VFR Aircraft Y a couple miles in trail of us landing on 22R. We both made calls and knew where each other was at. On a five mile final; Aircraft Z reported taxiing across 22R on taxiway Delta; planning an intersection takeoff on 22L at intersection of Delta. At the last minute; he then decided to takeoff on 4L. The Aircraft Y pilot jumped on him telling him there was traffic on close final for both 22L and 22R. Aircraft Z taxied clear of the runway on the north side of 22R on Delta. Once we landed and passed taxiway Delta; Aircraft Z pulled out on one of the runways (4L/22R) and departed causing Aircraft Y to go around when on short final. The Aircraft Y pilot wasn't pleased.About that time; Aircraft Y did a quick trip around the pattern and on short final Aircraft A decided to cross the runway in front of him. We were on our ramp by that point and Aircraft Y was a couple hundred feet on short final when he crossed in front of him.This place is going to have an accident in the near future.