Not all Achilles tears are created equal. Some are really bad, some not as bad. Therefore some heal better than others. The Rams have to decide just how bad, long term, that injury is. The answer to that will NOT be made public, Next as the preseason goes forward, does the brain trust think they are a complete enough team to win a Superbowl. If the answer is "yes" but they need a stud RB to round out the offense, they might trade as much as a 3rd to get one if the right guy was available. If they think that what they have is good enough, and with some reps will get better, then no they won't trade. But that doesn't mean that they might not pick up a vet player they like that has been cut.
I think the situation is very fluid and all doors are being left open. It's just that they don't feel panicky or have the need to jump on anything that's available right now. They apparently are satisfied to just let it play out over the 3 or 4 weeks and see what develops. I don't think that's a bad plan at all. I guarantee you they have their eye on 3 or 4 possibilities just in case, and likely most are currently on teams.
Don't be surprised that if they think they need long term help that LeVeon Bell isn't on their radar. He's low miles. Healthy. What happened to the electric Bell I don't know. If his head is right, he's probably a 4.0 ypc guy, but he gives you some size and a pretty good nose for the end zone.
On the other hand, McVay may prefer to have smaller but really fast guys and just run on speed, speed, and more speed. Like KC does for the most part.
We'll probably only know after the 2nd preseason game.