I don't think anyone other than you has raised the question of either of those players being regarded as bigger than the Club. And the players certainly have said or done nothing to suggest they think that way either. What most fans recognise is that both players contributed greatly to our Club and added to Motherwell FC on and off the pitch. Not that many players past and present have contributed to the extent they have.
Unlike a sad, few, fickle fans on here I would be delighted if Moult rattles in 30 goals this season, no matter who he scores them for and as long as they don't contribute to a defeat for us. I think that after his run of terrible injuries he deserves some good fortune. Many less determined players would have given up by now. Credit to him for that. I don't really think he will score those goals but I wish him well.
And my take on both players attempts to continue playing for us is that most fans were desperate for them to do themselves credit, but nobody was screaming out for them to get more game time when it was clear they were not fit and therefore not contributing to the team. In fact it was extremely depressing watching them try their utmost but fall short. Both were punts worth taking, but punts that did not work out. Maybe that does not suit your storyline but it is reality.
But here is a question for you. Given he is only 31, and if Moult comes through the entire season injury free and scores upwards of 15 league goals for Utd would you entertain his return next season at age 32? Won't be an option of course, because if he does prove the doubters wrong, then Utd will extend his contract and he will likely be back at Fir Park wearing their colours.