The last miner reward will be earned in 2140. It's a 110 year timeline. The miners will not transfers the ASICs to the other chains, the ASIC will be obsolete, broken or something.
But in 2139 the reward will be tiny, so it's better to worry sooner. A reduction from 6BTC to 0.06BTC is /100, that is like 8 halvings, that is like 32 year. Anyway, in 32 years the the current ASICs will be obsolete, broken or something.
Yes, the question is if Bitcoin can survive in 26 years, when the block subsidy will be below 0.05 BTC and its security will be 2 orders of magnitude lower than today, whenever demand for blockspace falls below capacity.
