While he was out for a few weeks you started to see Reynolds grow. Even Higbee seemed to step up a bit (minus the dropped TD vs Saints...but Kupp was back at that point).
Under the prior Kupp injury it was always known that Kupp was coming back. This time.....Reynolds, and the TE's will be expected to step up and fill a void heading into the playoffs. For that matter.....with Kupp likely being out until mid-2019 seaon, they can expect to get the spotlight for a while. It was also good that they didn't cut Nick Williams after Kupp returned.
No doubt that losing Kupp sucks. However, last year the Eagles lost Wentz and still made a run and won the Superbowl. There's no reason why the Rams can't do the same. Everyone else (particularly the defense) will need to step it up.
With respect to Kupp's return. His strength is not agility and speed. It is solid route running and good hands. Returning from an ACL should not cause his game to deteriorate.