While I don't entirely agree with the list of replacements, I think Richardson is an easy choice for me. He high points the ball, wins 50/50 balls despite not being a big guy, has very good deep speed, and would probably thrive by running good routes thrown to by Goff.
As for Watkins. If he is determined that he must be thought of as "the man"; or must get the wealth of targets; or if he sees himself as a true #1 WR in the mold the formerly-great Dez Bryant, AJ Green, Julio Jones, Antonio Brown, etc........then the Rams should not keep him at ANY price because he is not going to be happy. The ball WILL be spread around, and the attitude of one WR insisting he must get the most targets is the opposite of "We Not Me".
However, if Watkins can be a WR1.5 (NOT a WR1.0), be OK as part of a WR tool box, and be a happy wealthy man at $10 mil per year, I think he will remain a Ram and will be good for the team.
My gut tells me that Watkins feels he must be the man. And therefore wants "the man" money and attention.