General aviation pilot reported aborting the takeoff due to an aircraft with a loss of power landing on the runway.

Narrative

There were at least 7 planes in the pattern on 17 at S50; several PPL training flights; and at least 4 planes awaiting departure. Due to the high volume of traffic; traffic awaiting departure requested extended downwind legs to allow departures. The pattern was extended by at least a mile eventually; after repeated extensions of downwind; resulting in more than a two-mile final for landing aircraft in the pattern. This non-standard pattern resulted in at least 3 aircraft on final leg at one time. A fourth aircraft turned right base beyond the standard pattern; but short of the long extended pattern and conflicted with another aircraft on final. The aircraft already established on final executed a left 360; and the base to final traffic proceeded and completed their landing. After executing a 360; the previously established aircraft rejoined final and landed. The two pilots proceeded to argue over the radio for several minutes after both landed; preventing other communications; including pattern and take-off announcements. I observed this as the next departing aircraft; waiting to take off at the threshold; and spoke to the conflicting aircraft pilot afterward. Within the same hour; an aircraft lost power and safely executed a 180 to return to land 35. I was taking off 17 at the time; and safety aborted my take-off and made space for the landing aircraft. If it had been a student taking off under pressure of the busy pattern; they may not have been able to recognize the situation and safely clear.This is typical of conditions at S50; with many training aircraft based on field having been displaced from other local airports. There are often 7-8 aircraft in the pattern and/or joining on a 45; with patterns extending and becoming non-standard creating unpredictable conditions ripe for serious incidents.