A price of $252,000 in era 0 (50 BTC/block) would have caused the Bitcoin network to attempt to consume about 30% of all the electrical power produced on the planet.
A price of $252,000 in this era, era 1 (25 BTC/block) would cause the Bitcoin network to attempt to consume about 15% of all the electrical power produced on the planet.
So, in order to keep the Bitcoin network from attempting to consume more than 1% of all the power produced we should all hope that the price does not reach that level until at least era 5 - about 2029 or so.
Of course all of these numbers are rough "back of the envelope"
estimates:
Original target Subsidy Est Fees Power % of total world
Era starting year BTC/block BTC/hour GW power production
--- --------------- ----------- ---------- ------ ----------------
0 2009 50.00000000 0.00000000 680.40 29.44%
1 2013 25.00000000 0.00000000 340.20 14.72%
2 2017 12.50000000 0.00000000 170.10 7.36%
3 2021 6.25000000 0.00000000 85.05 3.68%
4 2025 3.12500000 0.00000000 42.53 1.84%
5 2029 1.56250000 0.00000000 21.26 0.92%
6 2033 0.78125000 1.31250000 13.61 0.59%
7 2037 0.39062500 3.65625000 13.61 0.59%
8 2041 0.19531250 4.82812500 13.61 0.59%
9 2045 0.09765625 5.41406250 13.61 0.59%
that only means old miners become valuable again, but there's no way mining manufacturers can build miners fast enough to actually produce enough miners to consume that much energy.
and even if they could, who would pay for all that? I mean paying up front, which is a risky thing knowing how mining manufacturers like to scam (BFL, Blackarrow, just to name a few)
but still i think 252k bitcoin is a few years too early