Missiles, yeah, it's not endless thing and considering that they don't make such massive attacks against Ukraine like they used before may be indicator that they can't produce it enough. But tanks, it won't end anytime soon. Recently they took out T-54/55 from storages (post WW2 tanks). Estimated numbers that they had 500-600 such tanks in reserve and storages. What's next? T-44 and T-34?
Tanks may not
disappear entirely (they do make a hundred or so T90s a year), but there is already a significant shortage even with the T62s and T55s being unpickled. First Ukrainian sources started reporting a few months ago that Russians are creating entire infantry battalions equipped mostly with transports (often not even armored vehicles but crap like "buhanka") and throwing those at the front line. Basically "meat". Now even Russian "voyenkors" are whining about it so it's mostly likely true.
Then you have tactical geniuses like the one who decided to attack Vuhledar and they lose half of their annual tank production in one battle.