It's probably not Philip Rivers' last year as a member of the San Diego Chargers. Hell, the team probably won't even finish as poorly in 2016 as they did in 2015.
However, it's interesting to note that the Chargers would actually save money next offseason by cutting Philip Rivers.
It's also worth noting that Rivers ranked 20th in QBR and and 11th in DVOA in 2015 while having the 2nd highest cap hit in the league among NFLs.
If the Chargers were to finish below .500 once again this season, a good argument could be made for the team moving on from Head Coach Mike McCoy. However, with a lengthy extension being given to Tom Telesco, there's almost no chance that he would be replaced as the team's General Manager.
Telesco would need to find a way to transition out of the era of Rivers and Gates, and jumpstart a new era of Chargers football. Cutting Rivers would be the easiest way to do that, and it would allow an incoming Head Coach to come in and pick his QB.
In the last five seasons, Rivers has posted exactly one season with a QB Rating over 100. The Chargers have been over .500 in just two of the last five seasons, and they haven't won more than 9 games since 2009. This team might be stuck in the "murky middle" of the NFL, although a high draft pick this year could help balanced that out a bit. If it doesn't, don't be shocked to see Tom Telesco looking for options to rebuild his team around a new franchise QB.