The first tie-breaker is Head-to-Head record between teams. The second tie-breaker is Division record. The third tie-breaker is Common Games record.
Even with a Denver WIN over Buffalo, the Chargers can finish with the same Overall record (Denver loses to Chiefs and Chargers win out) AND TIE both Head-to-Head (they split - First tie-breaker) AND Division Record (they'd both be 3-3 - 2nd tie-breaker).
The reason they are out if Denver wins is because it would then be mathematically impossible for the Chargers to tie Denver’s Common Games record (by exactly 1 game in fact). This scenario was further complicated by the fact both team's last two games ARE Common Games.
COMMON OPPONENTS (DEN / SDC):
OAK: L / L
Green Bay: L / L
New England: L / L
Miami: W / W
KCC: W / W
MIN: W / W
Jets: W / L
Chicago: W / L
Buffalo: ? / W
Detroit: L / ?
Oak: W / ?
KCC: ? / L
This illustrates that Denver has 2 more wins against common opponents, and the Chargers CAN tie the third tiebreaker if Denver loses out and the Chargers win out (understanding at THAT point the Chargers would simply have the better overall record at 9-7 while Denver would be 8-8).
However, if Denver beats the Bills they mathematically finish with one more win against common opponents than the Chargers can possibly have - even if the Chargers win out and Denver loses to the Chiefs at that point (they would both finish overall 9-7, split head-to-head and be 3-3 in the division in that scenario).
I was simply getting tired of hearing "tie-breakers DUH" as if that explained anything, not to mention the straight-up incorrect information I've been reading far too often.
If I missed anything here, please feel free to point it out, because I was having a difficult time understanding why the Chargers were automatically out with a Denver win over Buffalo.