Federer did not win a big title since 2012 - no one other than the Chinese has won big Titles since Samsonov in 2009. You think the fact that Federer got luck in 2017 now makes you right after the fact? Or you would have been wrong in Samsonov had beaten Mizutani despite being injured?
When he stops enjoying it, he will stop playing. Saive was the same way.
If he makes semis/finals consistently like Federer did since 2012 and consistently threatened the top guys for big titles. I would have been equally thrilled for Samsonov. Anyway, this is a fan's perspective. Till when he enjoys and plays the game is his own decision. But as a fan, I want him to win more games. I am not sure how many people enjoyed watching Waldner into late 40s. If that is the way Samsonov wants to go out, it is his wish but he will have one fan less among his legion of admirers.
Just in case anybody wants to review his performance last 6 months (or so) in major tournaments :
Qatar Open 2107- Round of 32
India Open - Round of 32
ITTF Europe Top 16 - Qualifying
Hungarian Open - Quarter Final (CNT sent their B team here)
World Tour Finals - Round of 16
European Table Tennis Championships 2016 - Round of 16
He won some challenger tournament but I think there was nobody else playing the event apart from unknown players.