Yes, if you're basing your decision on how those 18 games have gone, the style of football, the points gained, the progress or otherwise that's been made, as well as the direction of travel, how you see the manager performing next season, the players he thinks are needed or that he can obtain, etc.
However, the post I responded to suggested if we stay up he's done a great job, if we go down he deserves the sack for failure. Purely based on the outcome of Sunday. One football game, where anything could happen.
The decision on whether he stays or goes should not ride on 90 minutes of football. The bigger picture should drive the decision.