Riker and Garrett didn't look like they were getting up again
But many people injured like Jadzia Dax could have "gotten up again" with the help of the particles. Jadzia, after being attacked in the Temple, was taken to sick bay alive. Dying subsequently.
Not everyone on Star Trek dies right away. Could the particle help everyone, no. But you can't say that they wouldn't help anyone. This makes them an asset.
"Ran out" as in the amount they harvest runs out since the simulation kind of looks like the rings are destroyed meaning no new source of particles
It's difficult to see what your point is here. If the particles have a limited duration, then the environment of the ring planet's system would have been replenishing them in some fashion. Therefor if the particle you have lose effectiveness in time, you simply return to the original source, and get more.
However, if the particle's emissions are perpetual, then the Federation's particles will never "run out."
Remember Hartzilla, the particles didn't run out while in orbit of the ring planet, the last thing anybody would want to do is change the particle's emissions in the process of the harvest. So the particles in orbit, are the particles after harvest.