I'm not sure why you're bundling environmentalists in with anti-gun groups. These are two different areas, even if members of one are also the other.
I am in favour of guns, but am also a proponent of environmental protection initiatives: I think this a very important things and part of the legacy to hand on to future generations.
+1. Hear hear.
Oh, we WILL run out - it's when, not if. Might be 1000 years or 10,000 years, but..... We will also run out of everything else too - iron, copper, aluminum, magnesium, cobalt, tin, lithium, gold, silver, platinum, and all the others. Coal & oil too (sooner rather than later). Again, re-cyclable or not, it eventually all runs out... but it might be hundreds, thousands or tens of thousands of years - you just have to analyze each resource on a case by case basis. I'm not sure how much lead is left based upon anticipated population and economy growth worldwide, or even upon current consumption rates.
Chances are that a global pandemic, global acidity / co2 poisoning / warming dieoff, supervolcano, or earth-crossing meteor impact will kill of mankind first (greatly aided by war related to post-peak-oil / post-peak-coal era tensions), so I suppose it's possible "we" won't run out, since if "we" are no longer present here, "we" by definition cannot run out. But on the current course of population growth, or even much much less growth than actual, if continuing unabated, everything runs out. Heck, even with zero net growth, just staying at 7 billion, we'll run out eventually, but that 7 billion is growing exponentially.
Maybe some day, we will use earth moving equipment to take all the lead-filled dirt from all the gun ranges, replace it with "pure" dirt, and then send the lead-dirt to the recycling plant, to be sifted and reclaimed. Problem with that is, if it's more than a couple hundred years henceforth, we won't have any oil left to make gasoline with to run the equipment, so I suppose it won't matter a great deal.
But to answer your question, yes, fast and small rounds that rely upon expansion for terminal damage will become less useful and popular, and big and slow ones will become more useful and popular (so no, .45 acp will be more, not less, useful, relative to others like say, 9x19, which rely more upon expansion. As for .22, yes, any small bore would be of less killing power). Rifled "shotguns" would become extremely popular for hunting & defense, range limitations notwithstanding. Wider is better.