Answer:
Without a specific title or artist for the painting you are referring to, I can only provide a general answer.
However, based on the information you have provided, it is difficult to determine the artist's feelings about La Salle 150 years after his death from the imagery of a pirate ship going to sea with a sunset.
It is possible that the artist was not specifically referencing La Salle in the painting, and the imagery was intended to convey a general sense of adventure or exploration. Alternatively, the artist may have depicted the pirate ship and sunset to symbolize the end of an era or the passing of time, which could be interpreted in various ways depending on the artist's intent.
It is important to note that artwork can be interpreted in many different ways, and without additional context or information about the painting, it is difficult to make definitive conclusions about the artist's feelings towards La Salle.